543.二叉树的直径.cpp

/*
 * @lc app=leetcode.cn id=543 lang=cpp
 *
 * [543] 二叉树的直径
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int maxDiameter = 0;
    int diameterOfBinaryTree(TreeNode* root) {
        maxDepth(root);
        return maxDiameter;
    }

    int maxDepth(TreeNode* root) {
        if (root == nullptr) return 0;
        int left_max = maxDepth(root->left);
        int right_max = maxDepth(root->right);

        // 后序位置，顺便计算最大直径
        int my_diameter = left_max + right_max;
        maxDiameter = max(maxDiameter, my_diameter);
        return 1 + max(left_max, right_max);
    }
};
// @lc code=end