LeetCode:572. Subtree of Another Tree(判斷一棵樹是不是另外一棵樹的子樹)
阿新 • • 發佈:2018-12-10
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:(還是利用遞迴的方式)
/** * 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; } } }
時間複雜度:O(n^2)
空間複雜度:O(n)