543. Diameter of Binary Tree

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;
    }
};