629. K Inverse Pairs Array

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629. K Inverse Pairs Array

Given two integers n and k, find how many different arrays consist of numbers from 1 to n such that there are exactly k inverse pairs. We define an inverse pair as following: For ith and jth element in the array, if i < j and a[i] > a[j] then it's a…

【leetcode dp】629. K Inverse Pairs Array

https://leetcode.com/problems/k-inverse-pairs-array/description/ [题意] 给定n和k,求正好有k个逆序对的长度为n的序列有多少个,0<=k<=1000, 1<=n<=1000,答案模1e9+7 [思路] dp[i][j]表示正好有j个逆序对的长度为i的序列的方案数,最终我们要求的就是dp[n][k] 考虑dp[i+1][j]和dp[i][j]的关系,长度为i+1的序列相当于在长度为i的序列中插入一个数,那么有 xxx…

[LeetCode] K Inverse Pairs Array K个翻转对数组

Given two integers n and k, find how many different arrays consist of numbers from 1 to n such that there are exactly k inverse pairs. We define an inverse pair as following: For ith and jth element in the array, if i < j and a[i] > a[j] then it's a…

[Swift]LeetCode629. K个逆序对数组 | K Inverse Pairs Array

Given two integers n and k, find how many different arrays consist of numbers from 1 to n such that there are exactly k inverse pairs. We define an inverse pair as following: For ith and jthelement in the array, if i < j and a[i] > a[j] then it's an…

[leetcode-629-K Inverse Pairs Array]

Given two integers n and k, find how many different arrays consist of numbers from 1 to n such that there are exactly k inverse pairs. We define an inverse pair as following: For ith and jth element in the array, if i < j and a[i] > a[j] then it's a…

Java实现 LeetCode 629 K个逆序对数组（动态规划+数学）

629. K个逆序对数组给出两个整数 n 和 k,找出所有包含从 1 到 n 的数字,且恰好拥有 k 个逆序对的不同的数组的个数. 逆序对的定义如下:对于数组的第i个和第 j个元素,如果满i < j且 a[i] > a[j],则其为一个逆序对:否则不是. 由于答案可能很大,只需要返回答案 mod 109 + 7 的值. 示例 1: 输入: n = 3, k = 0 输出: 1 解释: 只有数组 [1,2,3] 包含了从1到3的整数并且正好拥有 0 个逆序对. 示例 2: 输入: n = 3…

Find the largest K numbers from array （找出数组中最大的K个值）

Recently i was doing some study on algorithms. A classic problem is to find the K largest(smallest) numbers from an array. I mainly studyed two methods, one is directly methold. It is an extension of select sort, always select the largest number from…