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.
方法1:(还是利用递归的方式)
/**
* 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 (s.val == t.val && isSame(s, t)) {
return true;
}
return isSubtree(s.left, t) || isSubtree(s.right, t);
}
private boolean isSame(TreeNode t1, TreeNode t2) {
if (t1 == null && t2 == null) {
return true;
} else if (t1 == null || t2 == null) {
return false;
}
if (t1.val == t2.val) {
return isSame(t1.left, t2.left) && isSame(t1.right, t2.right);
} else {
return false;
}
}
}
时间复杂度:O(n^2)
空间复杂度:O(n)