543. Diameter of Binary Tree

#### QUESTION:

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.

#### EXPLANATION:

1.每个节点的最远距离其实就是左边的最大深度+右边的最大深度

2.每个节点同时又会为上一个节点提供左或者右分支的最大深度+1的路径

#### SOLUTION:

``````public class Solution {
public int max_depth = 0;
public int diameterOfBinaryTree(TreeNode root) {
diameterOfBinaryTreeHelper(root);
return max_depth;
}
public int diameterOfBinaryTreeHelper(TreeNode root){
if(root ==null) return 0;
int left = diameterOfBinaryTreeHelper(root.left);
int right = diameterOfBinaryTreeHelper(root.right);
int cur = left+right;
max_depth = Math.max(cur,max_depth);
return Math.max(left,right)+1;
};
}
``````
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