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新增部分题目解答
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‎未整理/DFS/100.相同的树.cpp‎

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/*
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* @lc app=leetcode.cn id=100 lang=cpp
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*
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* [100] 相同的树
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* struct TreeNode {
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* int val;
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* TreeNode *left;
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* TreeNode *right;
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* TreeNode() : val(0), left(nullptr), right(nullptr) {}
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* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
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* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
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* };
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*/
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class Solution {
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public:
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bool isSameTree(TreeNode* p, TreeNode* q) {
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if (p == nullptr && q == nullptr) return true;
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if (p == nullptr || q == nullptr) return false;
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if (p->val != q->val) return false;
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return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
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}
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};
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// @lc code=end
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‎未整理/DFS/101.对称二叉树.cpp‎

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/*
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* @lc app=leetcode.cn id=101 lang=cpp
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*
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* [101] 对称二叉树
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* struct TreeNode {
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* int val;
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* TreeNode *left;
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* TreeNode *right;
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* TreeNode() : val(0), left(nullptr), right(nullptr) {}
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* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
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* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
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* };
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*/
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class Solution {
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public:
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bool isSymmetric(TreeNode* root) {
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return symmetric(root->left, root->right);
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}
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bool symmetric(TreeNode* p, TreeNode* q) {
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if (p == nullptr && q == nullptr) return true;
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if (p == nullptr || q == nullptr) return false;
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if (p->val != q->val) return false;
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return symmetric(p->left, q->right) && symmetric(p->right, q->left);
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}
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};
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// @lc code=end
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‎未整理/DFS/104.二叉树的最大深度.cpp‎

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/*
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* @lc app=leetcode.cn id=104 lang=cpp
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*
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* [104] 二叉树的最大深度
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* struct TreeNode {
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* int val;
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* TreeNode *left;
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* TreeNode *right;
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* TreeNode() : val(0), left(nullptr), right(nullptr) {}
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* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
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* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
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* };
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*/
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class Solution {
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public:
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int maxDepth(TreeNode* root) {
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if (root == nullptr) return 0;
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int a = maxDepth(root->left);
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int b = maxDepth(root->right);
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return max(a, b) + 1;
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}
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};
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// @lc code=end
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‎未整理/DFS/108.将有序数组转换为二叉搜索树.cpp‎

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/*
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* @lc app=leetcode.cn id=108 lang=cpp
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*
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* [108] 将有序数组转换为二叉搜索树
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* struct TreeNode {
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* int val;
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* TreeNode *left;
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* TreeNode *right;
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* TreeNode() : val(0), left(nullptr), right(nullptr) {}
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* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
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* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
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* };
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*/
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class Solution {
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public:
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TreeNode* sortedArrayToBST(vector<int>& nums) {
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return genBST(nums, 0, nums.size() - 1);
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}
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TreeNode* genBST(vector<int>& nums, int begin, int end) {
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if (begin > end) return nullptr;
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int mid = (end + begin) / 2;
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TreeNode* root = new TreeNode(nums[mid]);
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root->left = genBST(nums, begin, mid-1);
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root->right = genBST(nums, mid+1, end);
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return root;
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}
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};
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// @lc code=end
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‎未整理/DFS/110.平衡二叉树.cpp‎

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/*
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* @lc app=leetcode.cn id=110 lang=cpp
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*
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* [110] 平衡二叉树
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* struct TreeNode {
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* int val;
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* TreeNode *left;
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* TreeNode *right;
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* TreeNode() : val(0), left(nullptr), right(nullptr) {}
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* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
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* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
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* };
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*/
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class Solution {
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public:
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bool isBalanced(TreeNode* root) {
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if (root == nullptr) return true;
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return dfs(root) != -1;
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}
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int dfs(TreeNode* root) {
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if (root == nullptr)
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return 0;
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int a = dfs(root->left);
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int b = dfs(root->right);
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if (a == -1 || b == -1) return -1;
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if (abs(a-b) > 1) return -1;
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return max(a, b) + 1;
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}
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};
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// @lc code=end
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‎未整理/DFS/112.路径总和.cpp‎

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/*
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* @lc app=leetcode.cn id=112 lang=cpp
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*
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* [112] 路径总和
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* struct TreeNode {
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* int val;
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* TreeNode *left;
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* TreeNode *right;
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* TreeNode() : val(0), left(nullptr), right(nullptr) {}
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* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
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* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
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* };
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*/
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class Solution {
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public:
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bool hasPathSum(TreeNode* root, int targetSum) {
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int sum = 0;
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return traceback(root, targetSum, sum);
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}
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bool traceback(TreeNode* root, int targetSum, int sum) {
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if (root == nullptr) return false;
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if (root->left == nullptr && root->right == nullptr)
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return (sum + root->val) == targetSum;
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return traceback(root->left, targetSum, sum + root->val) ||
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traceback(root->right, targetSum, sum + root->val);
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}
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};
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// @lc code=end
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‎未整理/DFS/257.二叉树的所有路径.cpp‎

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/*
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* @lc app=leetcode.cn id=257 lang=cpp
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*
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* [257] 二叉树的所有路径
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* struct TreeNode {
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* int val;
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* TreeNode *left;
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* TreeNode *right;
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* TreeNode() : val(0), left(nullptr), right(nullptr) {}
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* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
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* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
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* };
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*/
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class Solution {
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public:
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vector<string> binaryTreePaths(TreeNode* root) {
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vector<string> ans;
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vector<TreeNode*> path;
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dfs(root, path, ans);
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return ans;
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}
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void dfs(TreeNode* root, vector<TreeNode*>& path, vector<string>& ans) {
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if (root == nullptr) return;
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if (root->left == nullptr && root->right == nullptr) {
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string s;
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for (auto node : path) {
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s =s + to_string(node->val) + "->";
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}
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s += to_string(root->val);
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ans.push_back(s);
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} else {
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path.push_back(root);
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dfs(root->left, path, ans);
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dfs(root->right, path, ans);
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path.pop_back();
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}
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}
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};
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// @lc code=end
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‎未整理/DFS/733.图像渲染.cpp‎

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/*
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* @lc app=leetcode.cn id=733 lang=cpp
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*
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* [733] 图像渲染
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*/
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// @lc code=start
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class Solution {
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public:
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vector<vector<int>> floodFill(vector<vector<int>>& image, int sr, int sc, int color) {
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int pixel = image[sr][sc];
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if (pixel == color)
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return image;
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dfs(image, sr, sc, pixel, color);
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return image;
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}
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void dfs(vector<vector<int>>& image, int i, int j, int pixel, int color) {
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// cout << i << " " << j << endl;
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if (i < 0 || j < 0)
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return;
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if (i >= image.size() || j >= image[0].size())
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return;
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if (image[i][j] == pixel) {
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image[i][j] = color;
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dfs(image, i-1, j, pixel, color);
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dfs(image, i+1, j, pixel, color);
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dfs(image, i, j-1, pixel, color);
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dfs(image, i, j+1, pixel, color);
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}
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}
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};
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// @lc code=end
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‎未整理/双指针/331.验证二叉树的前序序列化.cpp‎

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/*
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* @lc app=leetcode.cn id=331 lang=cpp
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*
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* [331] 验证二叉树的前序序列化
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*/
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// @lc code=start
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class Solution {
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public:
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bool isValidSerialization(string preorder) {
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}
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};
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// @lc code=end
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‎未整理/栈/1078.bigram-分词.cpp‎

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/*
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* @lc app=leetcode.cn id=1078 lang=cpp
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*
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* [1078] Bigram 分词
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*/
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// @lc code=start
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class Solution {
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public:
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vector<string> findOcurrences(string text, string first, string second) {
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vector<string> words = split(text, ' ');
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vector<string> ans;
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for (int i = 0; i < words.size() - 2; i++) {
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if (words[i] == first && words[i+1] == second) {
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ans.push_back(words[i+2]);
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}
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}
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return ans;
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}
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vector<string> split(const string& text, char sp) {
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vector<string> ans;
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string a = "";
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for (char c : text) {
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if (c == sp) {
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if (a != "")
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ans.push_back(a);
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a = "";
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continue;
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} else {
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a = a + c;
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}
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}
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if (a != "")
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ans.push_back(a);
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return ans;
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}
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};
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// @lc code=end
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