Description

Submission

/**
 * 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 {
    TreeNode* ret = nullptr;
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        dfs(root, p, q);
        return ret;
    }

    int dfs(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(!root) return 0;
        int left = dfs(root->left, p, q);
        int right = dfs(root->right, p, q);
        int cur = (root == p || root == q);
        int count = left + right + cur;
        if(count == 2 && !ret) ret = root;
        return count;
    }
};