236-二叉树的最近公共祖先.cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
static const auto __ = []()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    return nullptr;
}();
class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        //如果p，q就是root，那么祖先就是root，否则递归
        //如果p，q分别在左右子树，那么祖先就是root
        //如果在同一颗子树，继续递归
        if(root == NULL || root == p || root ==q) return root;
        TreeNode* left = lowestCommonAncestor(root->left, p, q);
        TreeNode* right = lowestCommonAncestor(root->right, p, q);
        if(left && right)
            return root;
        else
            return left == NULL ? right : left;
    }
};