543. Diameter of Binary Tree

description

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].

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

This problem is described below:

1 go through every node with recursive method and return the maximum length of per node
2 if left max length and right length is larger than than current length, then we change the current length.

implementation

The code is below:

/** * 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 getTheMaximumLength(TreeNode* root, int &len) {        if(!root) return 0;        int left_max = getTheMaximumLength(root->left, len) + 1;        int right_max = getTheMaximumLength(root->right, len) + 1;        len = max(left_max + right_max, len);        return max(left_max, right_max);    }    int diameterOfBinaryTree(TreeNode* root) {        int res = 0;        if(!root) return res;        getTheMaximumLength(root, res);        return res - 2;    }};