Leetcode-100 —— Same Tree

Description

Given two binary trees, write a function to check if they are the same or not.

Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

Example 1:

Input:     1         1
          / \       / \
         2   3     2   3

        [1,2,3],   [1,2,3]

Output: true

Example 2:

Input:     1         1
          /           \
         2             2

        [1,2],     [1,null,2]

Output: false

Example 3:

Input:     1         1
          / \       / \
         2   1     1   2

        [1,2,1],   [1,1,2]

Output: false

分析

处理树的问题一般都离不开递归的思想，我们先把问题分解为两个子问题，

1. 根节点相等
2. 两颗树的左子树和右子树分别相等

程序设计

基于以上分析不难写出代码，如下，

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null || q == null) {
            return p == q;
        }
        
        return p.val == q.val && isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    }
}

哈哈，提交后一遍过了，写了这么久终于实现了第一次 bugfree，值得纪念。