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Leetcode572-subtreeOfAnotherTree

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

Example

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.

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; }
* }
*/
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);
}

private 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);
}
}