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  • #Leetcode# 236. Lowest Common Ancestor of a Binary Tree

    https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/

    Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.

    According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).”

    Given the following binary tree:  root = [3,5,1,6,2,0,8,null,null,7,4]

    Example 1:

    Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1
    Output: 3
    Explanation: The LCA of nodes 5 and 1 is 3.
    

    Example 2:

    Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4
    Output: 5
    Explanation: The LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.
    

    Note:

    • All of the nodes' values will be unique.
    • p and q are different and both values will exist in the binary tree.

    代码:

    /**
     * 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) {
            if(!root || p == root || q == root) return root;
            TreeNode *left = lowestCommonAncestor(root -> left, p, q);
            TreeNode *right = lowestCommonAncestor(root -> right, p, q);
            if(left && right) return root;
            return left ? left : right;
        }
    };
    

      呜呜呜 今天在 PAT 甲级接连碰壁 总是差一点 AC 啊  刚开始看这个题似曾相识 仔细翻一下才发现上一个是二叉搜索树这个只是普通二叉树

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  • 原文地址:https://www.cnblogs.com/zlrrrr/p/10165813.html
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