[LeetCode]100. 相同的树

题目

100. 相同的树
给你两棵二叉树的根节点 p 和 q ，编写一个函数来检验这两棵树是否相同。

如果两个树在结构上相同，并且节点具有相同的值，则认为它们是相同的。

 

示例 1：


输入：p = [1,2,3], q = [1,2,3]
输出：true
示例 2：


输入：p = [1,2], q = [1,null,2]
输出：false
示例 3：


输入：p = [1,2,1], q = [1,1,2]
输出：false
 

提示：

两棵树上的节点数目都在范围 [0, 100] 内
-104 <= Node.val <= 104

方法1：DFS

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

方法2：BFS

    public boolean isSameTree(TreeNode p, TreeNode q) {
    
        if (p == null && q == null) return true;
        if (p == null || q == null) return false;
        Queue<TreeNode> queue1 = new LinkedList<>();
        Queue<TreeNode> queue2 = new LinkedList<>();
        queue1.offer(p);
        queue2.offer(q);
        while (!queue1.isEmpty()) {
    
            TreeNode currP = queue1.poll();
            TreeNode currQ = queue2.poll();
            if (currP == null && currQ == null) continue;
            if (currP.val != currQ.val) return false;
            TreeNode currPLeft = currP.left;
            TreeNode currPRight = currP.right;
            TreeNode currQLeft = currQ.left;
            TreeNode currQRight = currQ.right;
            if (currPLeft == null ^ currQLeft == null) return false;
            if (currPRight == null ^ currQRight == null) return false;
            if (currPLeft != null) queue1.offer(currPLeft);
            if (currPRight != null) queue1.offer(currPRight);
            if (currQLeft != null) queue2.offer(currQLeft);
            if (currQRight != null) queue2.offer(currQRight);
        }
        return true;
    }