572. Subtree of Another Tree[Easy]

572. Subtree of Another Tree

Given the roots of two binary trees root and subRoot, return true if there is a subtree of root with the same structure and node values of subRoot and false otherwise.

A subtree of a binary tree tree is a tree that consists of a node in tree and all of this node's descendants. The tree tree could also be considered as a subtree of itself.

Constraints:

• The number of nodes in the root tree is in the range [1, 2000].
• The number of nodes in the subRoot tree is in the range [1, 1000].
• -10^4 <= root.val <= 10^4
• -10^4 <= subRoot.val <= 10^4

Example
https://assets.leetcode.com/uploads/2021/04/28/subtree1-tree.jpg

Input: root = [3,4,5,1,2], subRoot = [4,1,2]
Output: true

思路

先去做100. Same Tree[Easy],再次基础上，加上遍历每一个节点，就能得出是否含有子树

题解

    public boolean isSubtree(TreeNode root, TreeNode subRoot) {
	// 如果目标子树为null 直接返回true
        if (subRoot == null)
            return true;
	// 如果当前遍历节点已为null 在目标子树不为null 的基础上，返回false
        if (root == null)
            return false;

        // 判断当前子树是否相等
        if (isSameTree(root, subRoot))
            return true;

        //没有命中结束条件就继续遍历
        return isSubtree(root.left, subRoot) || isSubtree(root.right, subRoot);
    }

    public boolean isSameTree(TreeNode n1, TreeNode n2) {
        if (n1 == null && n2 == null)
            return true;
        if ((n1 == null || n2 == null) || (n1.val != n2.val))
            return false;

        return isSameTree(n1.left, n2.left) && isSameTree(n1.right, n2.right);
    }