【DP】 HDOJ 1081 To The Max

#include <iostream>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <bitset>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <climits>
#include <cstdlib>
#include <cmath>
#include <time.h>
#define maxn 105
#define maxm 400005
#define eps 1e-10
#define mod 1000000007
#define INF 999999999
#define lowbit(x) (x&(-x))
#define mp mark_pair
#define ls o<<1
#define rs o<<1 | 1
#define lson o<<1, L, mid
#define rson o<<1 | 1, mid+1, R
//typedef vector<int>::iterator IT;
typedef long long LL;
//typedef int LL;
using namespace std;
LL qpow(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base;base=base*base;b/=2;}return res;}
LL powmod(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base%mod;base=base*base%mod;b/=2;}return res;}
void scanf(int &__x){__x=0;char __ch=getchar();while(__ch==' '||__ch=='\n')__ch=getchar();while(__ch>='0'&&__ch<='9')__x=__x*10+__ch-'0',__ch = getchar();}
LL gcd(LL _a, LL _b){if(!_b) return _a;else return gcd(_b, _a%_b);}
// head

int mat[maxn][maxn], sum[maxn][maxn];
int t[maxn], n;

void read(void)
{
for(int i = 1; i <= n; i++)
for(int j = 1; j <= n; j++)
scanf("%d", &mat[i][j]);
for(int i = 1; i <= n; i++)
for(int j = 1; j <= n; j++)
sum[j][i] = sum[j-1][i] + mat[j][i];
}
void work(void)
{
int ans = 0, res, mx;
for(int i = 1; i <= n; i++)
for(int j = i; j <= n; j++) {
for(int k = 1; k <= n; k++)
t[k] = sum[j][k] - sum[i-1][k];
res = mx = 0;
for(int k = 1; k <= n; k++) {
res += t[k];
if(res >= 0) mx = max(mx, res);
else {
if(t[k] >= 0) res = t[k];
else res = 0;
}
}
ans = max(ans, mx);
}
printf("%d\n", ans);
}
int main(void)
{
while(scanf("%d", &n)!=EOF) {
read();
work();
}
return 0;
}