如何找到最小ķ长度和最大和一个子？ [英] How to find a subarray with minimum k length and maximum sum?

问题描述

的子阵列同时包含正数和负数。你必须找到具有最大累加和子阵列，使得子阵列的长度大于或等于k

The subarray contains both positive and negative numbers. You have to find a maximum sum subarray such that the length of the sub-array is greater than or equal to k.

下面是我的code在C ++中使用Kadane算法。

Here is my code in c++ using Kadane's algorithm.

#include <iostream>

using namespace std;

int main(){

    int n,k;
    cin >> n >> k;
    int array[n];
    int sum = 0;
    int maxsum = 0;
    int beststarts[n];

    for(int i = 0;i < n; i++){
            cin >> array[i];
    }

    for(int i = 0;i < k-1;i ++){
            sum = sum+array[i];
            beststarts[i] = 0;
    }


    for(int i =  k-1;i < n; i++){ //best end search with min length;
            sum = sum+array[i];
            int testsum = sum;
            if(i > 0){
            beststarts[i] = beststarts[i-1];
            }
            for(int j = beststarts[i] ;i-j > k-1;j ++){
                    testsum = testsum - array[j];
                    if(testsum > sum){
                            beststarts[i] = j+1;
                            sum = testsum;
                    }
            }
            if(sum > maxsum){
                    maxsum = sum;
            }
    }

    cout << maxsum;

    return 0;
}

我的code是工作的罚款，但它是很慢的，我想不出任何办法来提高我的code。我也看到了这个问题的[Arrays]find最长子阵列，其总和整除被K 但是这不是我想要的，长度可大于k的也。

My code is working fine but it is very slow, and i cant think of any ways to improve my code. I have also read this question [Arrays]find longest subarray whose sum divisible by K but that is not what i want, the length can be greater than k also.

推荐答案

解决方案基于<一href="http://stackoverflow.com/questions/7861387/maximum-contiguous-subsequence-sum-of-at-least-length-l/7862283#7862283">this回答

现场演示

#include <algorithm>
#include <iterator>
#include <iostream>
#include <numeric>
#include <ostream>
#include <utility>
#include <vector>

// __________________________________________________

template<typename RandomAccessIterator> typename std::iterator_traits<RandomAccessIterator>::value_type
max_subarr_k(RandomAccessIterator first,RandomAccessIterator last,int k)
{
    using namespace std;
    typedef typename iterator_traits<RandomAccessIterator>::value_type value_type;
    if(distance(first,last) < k)
        return value_type(0);
    RandomAccessIterator tail=first;
    first+=k;
    value_type window=accumulate(tail,first,value_type(0));
    value_type max_sum=window, current_sum=window;
    while(first!=last)
    {
        window += (*first)-(*tail) ;
        current_sum = max( current_sum+(*first), window );
        max_sum = max(max_sum,current_sum);
        ++first;
        ++tail;
    }
    return max_sum;
}

// __________________________________________________

template<typename E,int N>
E *end(E (&arr)[N])
{
    return arr+N;
}

int main()
{
    using namespace std;
    int arr[]={1,2,4,-5,-4,-3,2,1,5,6,-20,1,1,1,1,1};
    cout << max_subarr_k(arr,end(arr),4) << endl;
    cout << max_subarr_k(arr,end(arr),5) << endl;
}

输出是：

14
11

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