Codeforces 372B Counting Rectangles is Fun

http://codeforces.com/problemset/problem/372/B

题意:每次给出一个区间，求里面有多少个矩形

思路:预处理，sum[i][j][k][l]代表以k,l为右下角，左上角不超过i,j有多少矩形，然后询问的时候枚举右下角就可以了

#include<cstdio>
#include<cmath>
#include<algorithm>
#include<cstring>
#include<iostream>
int n,m,T;
int sum[45][45][45][45],l[45][45];
char s[2005];
int read(){
    int t=0,f=1;char ch=getchar();
    while (ch<'0'||ch>'9'){if (ch=='-') f=-1;ch=getchar();}
    while ('0'<=ch&&ch<='9'){t=t*10+ch-'0';ch=getchar();}
    return t*f;
}
void init(){
    for (int i=1;i<=n;i++){
        scanf("%s",s+1);
        for (int j=1;j<=m;j++){
         if (s[j]=='1') continue;
         if (s[j-1]=='0') l[i][j]=l[i][j-1]+1;
         else l[i][j]=1; 
        }
    }
    for (int i=1;i<=n;i++)
     for (int j=1;j<=m;j++)
      for (int k=i;k<=n;k++)
       for (int L=j;L<=m;L++){
            int tmp=1<<29;
            int ss=0;
            for (int x=k;x>=i;x--){
                int ll=std::min(L-j+1,l[x][L]);
                tmp=std::min(tmp,ll);
                ss+=tmp;
            }
            sum[i][j][k][L]=ss;
       }
}
int main(){
    n=read();m=read();T=read();
    init();
    while (T--){
        int x1=read(),y1=read(),x2=read(),y2=read(),ans=0;
        for (int i=x1;i<=x2;i++)
         for (int j=y1;j<=y2;j++)
          ans+=sum[x1][y1][i][j];
        printf("%d
",ans);  
    }
    return 0;
}