LeetCode Same Tree
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.
思路分析:推断两个树是否同样,基本也非常easy想到用递归解。从root開始。不断递归比較两个树当前node的左孩子(右孩子),假设同一时候为空。返回true。否则仅仅有一个为空,还有一个不是空。返回false;当两个node都非空。我们比較它们的值,假设值不同,返回false。然后递归调用比較当前node的左孩子(右孩子)就可以。这里訪问顺序相当于root left right, 就是先序遍历,时间复杂度O(n),空间复杂度O(logn)(考虑递归调用栈保存空间大小)。
AC Code
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { public boolean isSameTree(TreeNode p, TreeNode q) { if(p == null && q == null) return true; if(p == null || q == null) return false;// only one of p and q is null if(p.val != q.val) return false; return isSameTree(p.left, q.left) && isSameTree(p.right, q.right); } }