二叉树的直径-树543-C++

算法思想：

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C++

/**
 * 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:
    
    int res = 1;

    int nodes_num(TreeNode * root){
        if(root == nullptr) return 0;
        int l = nodes_num(root->left);
        int r = nodes_num(root->right);
        res = max(res, l + r + 1);
        return max(l, r) + 1;
    }

    int diameterOfBinaryTree(TreeNode* root) {
        nodes_num(root);
        return res - 1;
    }
};