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.

计算树中任意两个节点之间的路径，要求路径最长

C++（12ms）：

/**
 * 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 diameterOfBinaryTree(TreeNode* root) {
        int res = 0 ;
        maxDepth(root,res) ;
        return res ;
        
    }
    
    int maxDepth(TreeNode* root , int& res){
        if (root == NULL) return 0 ;
        int left = maxDepth(root->left,res) ;
        int right = maxDepth(root->right,res) ;
        res = max(res , left+right) ;
        
        return 1 + max(left,right) ;
    }
};