计算二叉树的两个子节点距离最大值

Published: 20 Mar 2017 Category: algorithm

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;
    }
}

掌握:

  1. 递归求树的深度
  2. 算法思想