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Binary Tree Level Order Traversal II.cpp
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Binary Tree Level Order Traversal II.cpp
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/**
* Given a binary tree, return the bottom-up level order traversal of
* its nodes' values. (ie, from left to right, level by level from leaf to root).
*
* For example:
* Given binary tree {3,9,20,#,#,15,7},
* 3
* / \
* 9 20
* / \
* 15 7
* return its bottom-up level order traversal as:
* [
* [15,7]
* [9,20],
* [3],
* ]
*/
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<vector<int> > levelOrderBottom(TreeNode *root) {
vector<vector<int> > levels;
deque<TreeNode *> q_cur, q_next;
vector<int> t;
if (root == nullptr) {
return levels;
}
q_cur.push_back(root);
while (!q_cur.empty()) {
TreeNode *current = q_cur.front();
q_cur.pop_front();
t.push_back(current->val);
if (current->left != nullptr) {
q_next.push_back(current->left);
}
if (current->right != nullptr) {
q_next.push_back(current->right);
}
if (q_cur.empty()) {
q_cur = q_next;
q_next.clear();
levels.push_back(t);
t.clear();
}
}
vector<vector<int> > ret;
for (auto rit = levels.rbegin(); rit != levels.rend(); ++rit) {
ret.push_back(*rit);
}
return ret;
}
};