POJ-1050 To the Max

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题意

求最大子矩阵和。

题解

枚举列区间，将该区间的值压缩到一起，转化成求一维最大字段。

代码

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#include <cstring>
#include <ctime>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
#define ll long long
#define inf 0x3f3f3f3f
#define for0(i, n) for (int i = 0; i < n; i++)
#define for1(i, n) for (int i = 1; i <= n; i++)
#define forl(i, l, r) for (int i = l; i <= r; i++)
#define forn(i, n) for (int i = n; i >= 0; i--)
#define mem0(a) memset(a, 0, sizeof(a))
#define meminf(a) memset(a, inf, sizeof(a))
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  int n, a[101][101],b[101][101];
  cin >> n;
  mem0(b);
  for0(i, n) {
    for0(j, n){
      cin>>a[i][j];
      b[i][j+1]=b[i][j]+a[i][j];
    }
  }
  int ans=0;
  for0(i, n)
  forl(j, i+1, n){
    int tmp=0;
    for0(k, n){
      tmp+=b[k][j]-b[k][i];
      if (tmp<0) {
        tmp=0;
      }else if(tmp>ans){
        ans=tmp;
      }
    }
  }
  cout<<ans<<endl;
}