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

 1 #include<cstdio>
 2 #include<cmath>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<iostream>
 6 int n,m,T;
 7 int sum[45][45][45][45],l[45][45];
 8 char s[2005];
 9 int read(){
10     int t=0,f=1;char ch=getchar();
11     while (ch<‘0‘||ch>‘9‘){if (ch==‘-‘) f=-1;ch=getchar();}
12     while (‘0‘<=ch&&ch<=‘9‘){t=t*10+ch-‘0‘;ch=getchar();}
13     return t*f;
14 }
15 void init(){
16     for (int i=1;i<=n;i++){
17         scanf("%s",s+1);
18         for (int j=1;j<=m;j++){
19          if (s[j]==‘1‘) continue;
20          if (s[j-1]==‘0‘) l[i][j]=l[i][j-1]+1;
21          else l[i][j]=1;
22         }
23     }
24     for (int i=1;i<=n;i++)
25      for (int j=1;j<=m;j++)
26       for (int k=i;k<=n;k++)
27        for (int L=j;L<=m;L++){
28             int tmp=1<<29;
29             int ss=0;
30             for (int x=k;x>=i;x--){
31                 int ll=std::min(L-j+1,l[x][L]);
32                 tmp=std::min(tmp,ll);
33                 ss+=tmp;
34             }
35             sum[i][j][k][L]=ss;
36        }
37 }
38 int main(){
39     n=read();m=read();T=read();
40     init();
41     while (T--){
42         int x1=read(),y1=read(),x2=read(),y2=read(),ans=0;
43         for (int i=x1;i<=x2;i++)
44          for (int j=y1;j<=y2;j++)
45           ans+=sum[x1][y1][i][j];
46         printf("%d\n",ans);
47     }
48     return 0;
49 }