力扣534 二叉樹直徑 遞歸

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/**
 * 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 {
    int ans=0;
public:
    int dfs(TreeNode* root)
    {
        if(root==nullptr) return 0;
        int left=dfs(root->left);
        int right=dfs(root->right);
        ans=max(ans,left+right);
        return max(right,left)+1;
    }
    int diameterOfBinaryTree(TreeNode* root) {
        dfs(root);
        return ans;
    }
};