leetcode Ch4-Binary Tree & BFS & Divide/Conquer

一、 

1. Lowest Common Ancestor

 1 class Solution {
 2 public:
 3     TreeNode *lowestCommonAncestor(TreeNode *root, TreeNode *A, TreeNode *B) {
 4         if (root == NULL || root == A || root == B) {
 5             return root;
 6         }
 7         TreeNode* left = lowestCommonAncestor(root->left, A, B);
 8         TreeNode* right = lowestCommonAncestor(root->right, A, B);
 9         if (left != NULL && right != NULL) {
10             return root;
11         }
12         if (left != NULL) {
13             return left;
14         }
15         if (right != NULL) {
16             return right;
17         }
18         return NULL;
19     }
20 };

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