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面试题 04.10. 检查子树

English Version

题目描述

检查子树。你有两棵非常大的二叉树：T1，有几万个节点；T2，有几万个节点。设计一个算法，判断 T2 是否为 T1 的子树。

如果 T1 有这么一个节点 n，其子树与 T2 一模一样，则 T2 为 T1 的子树，也就是说，从节点 n 处把树砍断，得到的树与 T2 完全相同。

示例1:

 输入：t1 = [1, 2, 3], t2 = [2]
 输出：true

示例2:

 输入：t1 = [1, null, 2, 4], t2 = [3, 2]
 输出：false

提示：

1. 树的节点数目范围为[0, 20000]。

解法

Python3

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def checkSubTree(self, t1: TreeNode, t2: TreeNode) -> bool:
        def dfs(t1, t2):
            if t2 is None:
                return True
            if t1 is None:
                return False
            if t1.val == t2.val:
                return dfs(t1.left, t2.left) and dfs(t1.right, t2.right)
            return dfs(t1.left, t2) or dfs(t1.right, t2)

        return dfs(t1, t2)

Java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean checkSubTree(TreeNode t1, TreeNode t2) {
        if (t2 == null) {
            return true;
        }
        if (t1 == null) {
            return false;
        }
        if (t1.val == t2.val) {
            return checkSubTree(t1.left, t2.left) && checkSubTree(t1.right, t2.right);
        }
        return checkSubTree(t1.left, t2) || checkSubTree(t1.right, t2);
    }
}

C++

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool checkSubTree(TreeNode* t1, TreeNode* t2) {
        if (!t2) return 1;
        if (!t1) return 0;
        if (t1->val == t2->val) return checkSubTree(t1->left, t2->left) && checkSubTree(t1->right, t2->right);
        return checkSubTree(t1->left, t2) || checkSubTree(t1->right, t2);
    }
};

Go

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func checkSubTree(t1 *TreeNode, t2 *TreeNode) bool {
	if t2 == nil {
		return true
	}
	if t1 == nil {
		return false
	}
	if t1.Val == t2.Val {
		return checkSubTree(t1.Left, t2.Left) && checkSubTree(t1.Right, t2.Right)
	}
	return checkSubTree(t1.Left, t2) || checkSubTree(t1.Right, t2)
}

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