Add C++ solution for leetcode 993.

Author: yanglr

cpp-leetcode/leetcode993-cousins-in-binary-tree_dfs.cpp

@@ -0,0 +1,59 @@
+#include<vector>
+#include<algorithm>
+#include<iostream>
+#include<unordered_map>
+using namespace std;
+/**
+ * Definition for a binary tree node.
+ */ 
+struct TreeNode {
+    int val;
+    TreeNode *left;
+    TreeNode *right;
+    TreeNode() : val(0), left(nullptr), right(nullptr) {}
+    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+    TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+};
+
+class Solution {
+public:
+    bool isCousins(TreeNode* root, int x, int y) {
+        unordered_map<int, int> depths;  /* map: value -> depth */
+        unordered_map<int, int> parents; /* map: value -> parent value */
+        dfs(root, 0, depths, parents);
+        if (depths[x] == depths[y] && parents[x] != parents[y])
+            return true;
+        return false;
+    }
+    void dfs(TreeNode* root, int depth, unordered_map<int, int>& depths, unordered_map<int, int>& parents)
+    {
+        if (root == nullptr) return;
+        depths[root->val] = depth;
+        if (root->left != nullptr)
+        {
+            parents[root->left->val] = root->val;
+            dfs(root->left, depth + 1, depths, parents);
+        }
+        if (root->right != nullptr)
+        {
+            parents[root->right->val] = root->val;
+            dfs(root->right, depth + 1, depths, parents);
+        }
+        return;
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    TreeNode* root = new TreeNode(1);
+    root->left = new TreeNode(2);
+    root->right = new TreeNode(3);
+    root->left->right = new TreeNode(4);
+    root->right->right = new TreeNode(5);
+    auto res = sol.isCousins(root, 2, 3);
+    cout << (res ? "True" : "False") << endl;
+
+    return 0;
+}