USACO 5.3 Big Barn(DP）

最大子矩阵问题，USACO上貌似好几个把。。

 1 /*

 2 ID: cuizhe

 3 LANG: C++

 4 TASK: bigbrn

 5 */

 6 #include <iostream>

 7 #include <cstring>

 8 #include <cstdio>

 9 #include <cstdlib>

10 using namespace std;

11 int dp[1001][1001],r[1001][1001],c[1001][1001];

12 bool o[1001][1001];

13 int main()

14 {

15     int n,m,x,y,maxz,i,j;

16     freopen("bigbrn.in","r",stdin);

17     freopen("bigbrn.out","w",stdout);

18     scanf("%d%d",&n,&m);

19     for(i = 1;i <= m;i ++)

20     {

21         scanf("%d%d",&x,&y);

22         o[x][y] = 1;

23     }

24     for(x = 1;x <= n;x ++)

25     {

26         for(y = 1;y <= n;y ++)

27         {

28             if(o[x][y])

29             {

30                 r[x][y] = 0;

31                 c[x][y] = 0;

32                 dp[x][y] = 0;

33             }

34             else

35             {

36                 r[x][y] = r[x-1][y] + 1;

37                 c[x][y] = c[x][y-1] + 1;

38                 dp[x][y] = min(min(r[x][y],c[x][y]),dp[x-1][y-1]+1);

39             }

40         }

41     }

42     maxz = 0;

43     for(i = 1;i <= n;i ++)

44     {

45         for(j = 1;j <= n;j ++)

46         {

47             maxz =max(dp[i][j],maxz);

48         }

49     }

50     printf("%d\n",maxz);

51     return 0;

52 }