Subtree of Another Tree

投稿日 |

Description

Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node’s descendants. The tree s could also be considered as a subtree of itself.

Method

s是母树，t是子树，首先要在母树里找到子树的root节点。这里可以用递归的方法，从root节点往下查找。然后需要判断节点之后的树是否为s的子树。可以比较头结点的值然后递归比较子节点。

Solution

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