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
Return false.
题意：找一个树的子树
这里注意一点就行了，必须是子树不能是相同结构的情况
递归判断即可
class Solution { private boolean helper(TreeNode s, TreeNode t) { if (t != null && s == null) return false; if (t == null && s == null) return true; if (t == null && s != null) return false; if (t.val != s.val) return false; return helper(s.right, t.right) && helper(s.left, t.left); } public boolean isSubtree(TreeNode s, TreeNode t) { if (s == null) return false; boolean flag = false; if (s.val == t.val) flag = helper(t, s); return isSubtree(s.left, t) || isSubtree(s.right, t) || flag; } }