2020.7.15 刷
阿新 • • 發佈:2020-07-15
96. 不同的二叉搜尋樹
自己用dp寫的哈哈哈不是很整潔
class Solution { public int numTrees(int n) { int[] res = new int[n + 1]; if(n == 1)return 1; if(n == 2)return 2; res[0] = 1; res[1] = 1; res[2] = 2; for (int i = 3; i <= n; i++) { for (int j = 1; j <= i / 2; j++) { res[i]+= res[i - j] * res[j - 1]; } res[i] *= 2; if(i % 2 == 1) res[i] += res[(i - 1) / 2] * res[(i - 1) / 2]; } return res[n]; } }
貼個思路卡特蘭數
class Solution { public int numTrees(int n) { int[] dp = new int[n+1]; dp[0] = 1; dp[1] = 1; for(int i = 2; i < n + 1; i++) for(int j = 1; j < i + 1; j++) dp[i] += dp[j-1] * dp[i-j]; return dp[n]; } } 作者:guanpengchn 連結:https://leetcode-cn.com/problems/unique-binary-search-trees/solution/hua-jie-suan-fa-96-bu-tong-de-er-cha-sou-suo-shu-b/來源:力扣(LeetCode) 著作權歸作者所有。商業轉載請聯絡作者獲得授權,非商業轉載請註明出處。
在貼個python程式碼
class Solution: def numTrees(self, n: int) -> int: dp = [1, 1, 2] for i in range (3, n + 1): res = 0 for j in range (1, (int)(i/2 + 1)): res += dp[j - 1] * dp[i - j] res *= 2 if i % 2 == 1: res += dp[(int)((i-1)/ 2)] ** 2 dp.append(res) return dp[n]