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hdu 1081 To The Max
最大子矩阵和……
一直听说dp啊什么……
好吧……暴力
一个很巧妙的思想
由于有负数肯定是不太好的
所以,a[i][j]:第i行前j个数的和
然后,从第1行开始到最后一行,枚举第i列跟第j列(j<i),与第k行围起来的矩阵和,
用t记录当前结果,若t为负数,则t=a[k][i]-a[k][j]
若t为正数,t+=a[k][i]-a[k][j]
每次更新t后,更新答案ans即可
#include<iostream> #include<map> #include<string> #include<cstring> #include<cstdio> #include<cstdlib> #include<cmath> #include<queue> #include<vector> #include<algorithm> using namespace std; int a[1000][1000]; const int inf=1<<31; int main() { int i,j,k,n,t,ans; while(cin>>n) { memset(a,0,sizeof(a)); for(i=1;i<=n;i++) for(j=1;j<=n;j++) { cin>>t; a[i][j]=a[i][j-1]+t; } ans=inf; for(i=1;i<=n;i++) for(j=0;j<i;j++) { t=-1; for(k=1;k<=n;k++) { if(t<0) t=a[k][i]-a[k][j]; else t+=a[k][i]-a[k][j]; ans=max(ans,t); } } cout<<ans<<endl; } return 0; }
To The Max
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)Total Submission(s): 8571 Accepted Submission(s): 4161
Problem Description
Given a two-dimensional array of positive and negative integers, a sub-rectangle is any contiguous sub-array of size 1 x 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.
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 x 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
Greater New York 2001
hdu 1081 To The Max
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