LeetCode 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].

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

算法分析:

对根节点递归计算左右子树的Diameter，通过和类内的变量 diameter 进行比较，保存较大值。在每一次递归结束后，返回这棵子树的深度，根节点获取了左右子树的深度后，将二者相加就是该根节点下的Diameter。

Java算法实现：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    int diameter=0;
    public int diameterOfBinaryTree(TreeNode root) {
    	diameter=0;
        getDepth(root);
        return diameter;
    }
    
    public int getDepth(TreeNode root){
    	if(root==null){
    		return -1;
    	}
    	int leftDepth=getDepth(root.left);
    	int rightDepth=getDepth(root.right);
    	int temp=leftDepth+rightDepth+2;
    	if(temp>diameter){
    		diameter=temp;
    	}
    	return Math.max(leftDepth, rightDepth)+1;
    }
}