(LeetCode) 543. Diameter of Binary Tree

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 longest path 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].

思路

题干中所求的路径可以转化为求左右子树中最大的深度之和，所以在求树的深度的过程中保留最大的深度之和，即可求得结果。

代码

class Solution {
public:
    int diameterOfBinaryTree(TreeNode* root) {
        int result = 0;
        dps(root, result);
        return result;
    }


    int dps(TreeNode* root, int &result){
        if (root==NULL) return 0;
        int ld = dps(root->left, result) ;
        int rd = dps(root->right, result);
        result = max(ld + rd, result);
        return max(ld+1, rd+1);
    }
};