LeetCode Same Tree
2015-03-19 04:04
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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:判断两个树是否相同,基本也很容易想到用递归解。从root开始,不断递归比较两个树当前node的左孩子(右孩子),如果同时为空,返回true;否则只有一个为空,另一个不是空,返回false;当两个node都非空,我们比较它们的值,如果值不同,返回false。然后递归调用比较当前node的左孩子(右孩子)即可。这里访问顺序相当于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); } }
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