题目

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

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

附：结点定义如下

/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */

思路

这一题是一个简单的递归算法：如果两个树都为空，则返回true；如果一个空一个非空，则返回false；如果两个树的值不同，则返回false；如果相等，则递归比较两棵树的左右子树。

代码

public class Solution { public boolean isSameTree(TreeNode p, TreeNode q) { if(p==null && q == null) return true; if((p == null && q != null ) || (p != null && q == null)) return false; if(p.val == q.val) { if((p.left == null && q.left != null) || (p.left != null && q.left == null)) return false; if((p.right == null && q.right != null) || (p.right != null && q.right == null)) return false; if(p.left == null && p.right == null) return true; if(p.left != null && p.right == null) return isSameTree(p.left , q.left); if(p.right != null && p.left == null) return isSameTree(p.right , q.right); else{ return (isSameTree(p.left , q.left) && isSameTree(p.right , q.right)); } } return false; } }