To the Max
Description
Given a two-dimensional array of positive and negative integers, a sub-rectangle is any contiguous sub-array of size 1*1 or greater located within the whole array. The sum of a rectangle is the sum of all the elements in that rectangle. In this problem the sub-rectangle with the largest sum is referred to as the maximal sub-rectangle.
As an example, the maximal sub-rectangle of the array: 0 -2 -7 0 9 2 -6 2 -4 1 -4 1 -1 8 0 -2 is in the lower left corner: 9 2 -4 1 -1 8 and has a sum of 15. Input
The input consists of an N * N array of integers. The input begins with a single positive integer N on a line by itself, indicating the size of the square two-dimensional array. This is followed by N^2 integers separated by whitespace (spaces and newlines). These are the N^2 integers of the array, presented in row-major order. That is, all numbers in the first row, left to right, then all numbers in the second row, left to right, etc. N may be as large as 100. The numbers in the array will be in the range [-127,127].
Output
Output the sum of the maximal sub-rectangle.
Sample Input 4 0 -2 -7 0 9 2 -6 2 -4 1 -4 1 -1 8 0 -2 Sample Output 15 Source |
[Submit] [Go Back] [Status] [Discuss]
题解:dp
f[i][j][k]表示以i,j为右下角,向上延伸k行的最大子矩阵。
f[i][j][k]=max(f[i][j-1][k]+sum[i][j]-sum[i-k][j],sum[i][j]-sum[i-k][j])
其中sum[i][j]表示的是j列前i行的前缀和。
#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
#include<cmath>
#define N 103
using namespace std;
int f[N][N][N],n,m,sum[N][N],a[N][N];
int main()
{
scanf("%d",&n);
for (int i=1;i<=n;i++)
for (int j=1;j<=n;j++) scanf("%d",&a[i][j]);
for (int i=1;i<=n;i++)
for (int j=1;j<=n;j++)
sum[i][j]=sum[i-1][j]+a[i][j];
memset(f,128,sizeof(f));
int ans=f[0][0][0];
for (int i=1;i<=n;i++)
for (int j=1;j<=n;j++)
for (int k=1;k<=i;k++)
f[i][j][k]=max(f[i][j-1][k]+sum[i][j]-sum[i-k][j],sum[i][j]-sum[i-k][j]),ans=max(ans,f[i][j][k]);
printf("%d\n",ans);
}