[leetcode]572. 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:
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:
Given tree s:

     3    / \   4   5  / \ 1   2    /   0

Given tree t:

   4  / \ 1   2

思路:先序遍历，将树存到StringBuilder里，

Solution:

package com.billkang;class TreeNode {int val;TreeNode left;TreeNode right;TreeNode(int x) {val = x;}}/** * @author binkang * @date May 21, 2017 */public class SubtreeofAnotherTree {public boolean isSubtree(TreeNode s, TreeNode t) {StringBuilder sbd1 = new StringBuilder();StringBuilder sbd2 = new StringBuilder();preOrder(sbd1, s);preOrder(sbd2, t);return sbd1.toString().contains(sbd2);}private void preOrder(StringBuilder sbd, TreeNode t) {if(t == null) {sbd.append(",,");return;}sbd.append(",").append(t.val);preOrder(sbd, t.left);preOrder(sbd, t.right);}}