543. Diameter of Binary Tree（ 二叉树的直径）

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Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the longestpath between any two nodes in a tree. This path may or may not pass through the root.

Example:
Given a binary tree 

          1
         / \
        2   3
       / \     
      4   5    

 

Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

 

 

 

 

 

 

class Solution {
public:
    int res = 0;
    int dfs(TreeNode* root) {
        if (root==nullptr) return 0;
        int left = dfs(root->left);
        int right = dfs(root->right);
        res = max(res, left+right+1);
        return max(left,right) + 1;
    }
    int diameterOfBinaryTree(TreeNode* root) {
        // res 记录的是节点个数， 直径=节点个数-1
        dfs(root);
        return res-1;
    }
};