LeetCode: Subtree of Another Tree

LeetCode: Subtree of Another Tree

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.

Example 1:

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Given tree s:

     3
    / \
   4   5
  / \
 1   2
Given tree t:
   4
  / \
 1   2
Return true, because t has the same structure and node values with a subtree of s.

Example 2:

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Given tree s:

     3
    / \
   4   5
  / \
 1   2
    /
   0
Given tree t:
   4
  / \
 1   2
Return false.
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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) {
        Queue<TreeNode> queue = new LinkedList<>();

        queue.add(s);
        while (!queue.isEmpty()) {
            TreeNode node = queue.poll();
            if (isSame(node, t)) return true;
            if (node.left != null) queue.add(node.left);
            if (node.right != null) queue.add(node.right);
        }
        return false;
    }

    public boolean isSame(TreeNode s, TreeNode t) {
        if (s == null && t == null) return true;
        if (s == null || t == null || s.val != t.val) {
            return false;
        }
        return isSame(s.left, t.left) && isSame(s.right, t.right);
    }
}