最大子数组分治方案C++实现

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以下实现最大子数组的分治策略，算法来自《算法导论》

#include<iostream>

using namespace std;
 

struct ans

{

    int low;

    int high;

    int sum;

};

 

ans MAXIMUM_CROSSING_SBUARRAY(int * A, int low, int mid, int high)

{

    ans cross_ans = {mid, mid, INT_MIN};

    ans cross_left = {mid, mid, INT_MIN};

    ans cross_right = {mid + 1, mid + 1, INT_MIN};

    int sum = 0;

    for(int i = mid; i >= low; --i)

    {

        sum += A[i];

        if(cross_left.sum < sum)

        {

            cross_left.sum = sum;

            cross_left.low = i;

        }

    }

    sum = 0;

    for (int j = mid + 1; j <= high; ++j)

    {

        sum += A[j];

        if(cross_right.sum < sum)

        {

            cross_right.sum = sum;

            cross_right.high = j;

        }

    }

    cross_ans.low = cross_left.low;

    cross_ans.high = cross_right.high;

    cross_ans.sum = cross_left.sum + cross_right.sum;

    return cross_ans;

}

 

ans MAXIMUM_SUBARRAY(int * A, int low, int high)

{

    if(low == high)

    {

        ans myans = {low, high, A[low]};

        return myans;

    }

    else

    {

        int mid = (low + high) / 2;

        ans leftans = MAXIMUM_SUBARRAY(A, low, mid);

        ans rightans = MAXIMUM_SUBARRAY(A, mid + 1, high);

        ans crossans = MAXIMUM_CROSSING_SBUARRAY(A, low, mid, high);

        if(leftans.sum > rightans.sum && leftans.sum > crossans.sum)

            return leftans;

        else if(rightans.sum > leftans.sum && rightans.sum > crossans.sum)

            return rightans;

        else

            return crossans;

    }

}
 

int main()

{

    int b[] = {3, -2, 5, -7, 3, 1, 1,-4, 9, -3};

    ans mybestans = MAXIMUM_SUBARRAY(b, 0, 9);

    cout << "The sub_array's elements of b with the greatest sum is the element from "<< mybestans.low << " to " << mybestans.high << endl;

    cout << "The sum is " << mybestans.sum << endl;

    return 0;

}