leetcode 543. Diameter of Binary Tree

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].

Note: The length of path between two nodes is represented by the number of edges between them.

class Solution {
public:
    int maxLength(TreeNode *t,int &path)
    {
        if(t==NULL)
            return 0;
        int left=maxLength(t->left,path);
        int right=maxLength(t->right,path);
       
        path=max(right+left,path);
        return max(left+1,right+1);
        
    }
    int diameterOfBinaryTree(TreeNode* root) {
        if(root==NULL)
            return 0;
        int path=0;
        maxLength(root,path);
        return path;
        
    }
};

思路：

即求每个顶点左右子树相加的最大长度。