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.
题意：给出两个二叉树，判断这两个树是不是相等
思路：用DFS，首先比较当前结点的值是不是相等，然后比较左子树，再比较右子树

/**
* 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;
else if (p == null && q != null) return false;
else if (p != null && q == null) return false;
else {
if (p.val != q.val) return false;

if (!isSameTree(p.left, q.left) || !isSameTree(p.right, q.right)) return false;

return true;
}
}
}

第二种方法：用非递归方法，模拟递归的出栈、入栈

/**
* 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) {
Queue<TreeNode> q1 = new LinkedList<TreeNode>();
Queue<TreeNode> q2 = new LinkedList<TreeNode>();

q1.add(p);
q2.add(q);

while (!q1.isEmpty() && !q2.isEmpty()) {
TreeNode node1 = q1.poll();
TreeNode node2 = q2.poll();
if (node1 == null && node2 == null) continue;

if (node1 == null || node2 == null) return false;

if (node1.val != node2.val) return false;

q1.add(node1.left); q2.add(node2.left);
q1.add(node1.right); q2.add(node2.right);
}

return true;
}
}