LCA of Binary Tree: dfs.

Author: DeanChensj

Medium/236_Lowest-Common-Ancestor-of-a-Binary-Tree.cpp

@@ -0,0 +1,24 @@
+#include "../Header.h"
+#include "../TreeNode.h"
+
+using namespace std;
+TreeNode * LCA = nullptr;
+char helper(TreeNode* root, TreeNode* p, TreeNode* q) {
+    char flag = 0;
+    if (root->left) flag |= helper(root->left, p, q);
+    if (root->right) flag |= helper(root->right, p, q);
+    if (root == p) flag |= 2;
+    if (root == q) flag |= 1;
+    if (flag  == 3) {
+        LCA = root;
+        return 0;
+    } else return flag;
+}
+
+TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
+    if (!p) return q;
+    if (!q) return p;
+    helper(root, p, q);
+    return LCA;
+}
+