Create 1644.Lowest-Common-Ancestor-of-a-Binary-Tree-II.cpp

Tree/1644.Lowest-Common-Ancestor-of-a-Binary-Tree-II/1644.Lowest-Common-Ancestor-of-a-Binary-Tree-II.cpp

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+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) 
+    {
+        vector<TreeNode*>path1 = dfs(root, p);
+        reverse(path1.begin(), path1.end());
+
+        vector<TreeNode*>path2 = dfs(root, q); 
+        reverse(path2.begin(), path2.end());
+
+        if (path1.size()==0 ||path2.size()==0)
+            return NULL;
+
+        int i=0;
+        while (i<path1.size() && i<path2.size() && path1[i]==path2[i])
+            i++;
+        return path1[i-1];        
+
+    }
+
+    vector<TreeNode*>dfs(TreeNode* root, TreeNode* p)
+    {
+        if (root==NULL) return {};
+        if (root==p) return {root};
+        vector<TreeNode*>path = dfs(root->left, p);
+        if (!path.empty())
+        {
+            path.push_back(root);
+            return path;
+        }
+        path.clear();
+        path = dfs(root->right, p);
+        if (!path.empty())
+        {
+            path.push_back(root);
+            return path;
+        }
+        return {};
+    }
+};