343. 整数拆分
题目链接:343. 整数拆分 - 力扣(LeetCode)
动态规划法:
class Solution {public int integerBreak(int n) {int[] dp = new int[n+1];if(n <= 3) {return n - 1;}dp[0] = 0;dp[1] = 1;dp[2] = 2;dp[3] = 3;for(int i = 4; i < n + 1; ++i) {int max = 0;for(int j = 1; j < i/2 + 1; ++j) {max = Math.max(max, dp[i-j]*dp[j]);}dp[i] = max;}return dp[n];}
}
数学法(居然是自己想出来的):
class Solution {public int integerBreak(int n) {if(n <= 3) {return n - 1;}if(n % 3 == 0) {return (int)Math.pow(3, n/3);}else if(n % 3 == 1) {return (int)(4 * Math.pow(3, (n-4)/3));}else {return (int)(2 * Math.pow(3, (n-2)/3));}}
}
96.不同的二叉搜索树
题目链接:96. 不同的二叉搜索树 - 力扣(LeetCode)
class Solution {public int numTrees(int n) {int dp[] = new int[n + 1];if(n <= 2) {return n;}dp[0] = 1;dp[1] = 1;dp[2] = 2;for(int i = 3; i < n+1; ++i) {for(int j = 1; j <= i; ++j) {dp[i] += dp[j-1] * dp[i -j];}}return dp[n]; }
}