编程之美 子数组之和的最大值(二维)

#include <iostream>
using namespace std;

int PS[4][5];

void calculateBound(int B[3][4], int N, int M)
{
	int i, j;
	for (i = 0; i <= N; i++)
	{
		PS[i][0] = 0;
	}
	for (j = 0; j <= M; j++)
	{
		PS[0][j] = 0;
	}
	for (i = 1; i <= N; i++)
	{
		for (j = 1; j <= M; j++)
		{
			PS[i][j] = PS[i-1][j] + PS[i][j-1] - PS[i-1][j-1] + B[i-1][j-1];
		}
	}
}

int BC(int a, int c, int m)
{
	return (PS[c][m]-PS[a-1][m]-PS[c][m-1]+PS[a-1][m-1]);
}

int maxSum(int B[3][4], int N, int M)
{
	int arrayMaxSum = INT_MIN;
	int i, j, k;
	int arrayStart, arrayAll;
	for (i = 1; i <= N; i++)
	{
		for (j = i; j <= N; j++)
		{
			arrayStart = BC(i, j, M);
			arrayAll = BC(i, j, M);
			for (k = M-1; k >= 1; k--)
			{
				if (arrayStart < 0)
				{
					arrayStart = 0;
				}
				arrayStart += BC(i, j, k);
				if (arrayStart > arrayAll)
				{
					arrayAll = arrayStart;
				}
			}
			if (arrayAll > arrayMaxSum)
			{
				arrayMaxSum = arrayAll;
			}
		}
	}
	return arrayMaxSum;
}

int main()
{
	int N = 3;
	int M = 4;
	int A[3][4] = {1, 2, 3, 4, -4, 5, 6, 7, 0, 11, 23, 45};
	calculateBound(A, 3, 4);
	cout<<maxSum(A, N, M);
}