USACO 3.1 Stamps

和前边的一个题目求前缀那个很像，加上一个标记数组就行。

 1 /*

 2    ID: cuizhe

 3    LANG: C++

 4    TASK: contact

 5  */

 6 #include <cstdio>

 7 #include <cstring>

 8 #include <iostream>

 9 #include <queue>

10 #include <map>

11 using namespace std;

12 #define N 200001

13 int dp[2000001],p[500];

14 bool o[2000001];

15 int Min(int a,int b)

16 {

17     return a > b ? b:a;

18 }

19 int main()

20 {

21     int i,j,n,k;

22     //freopen("stamps.in","r",stdin);

23     //freopen("stamps.out","w",stdout);

24     scanf("%d%d",&k,&n);

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

26     {

27         scanf("%d",&p[i]);

28         o[p[i]] = 1;

29         dp[p[i]] = 1;

30     }

31     for(i = 1;;i ++)

32     {

33         if(o[i]&&dp[i] < k)

34         {

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

36             {

37                 o[i+p[j]] = 1;

38                 if(dp[i+p[j]] == 0)

39                 dp[i+p[j]] = dp[i]+1;

40                 else

41                 dp[i+p[j]] = Min(dp[i]+1,dp[i+p[j]]);

42             }

43         }

44         else if(!o[i])

45         {

46             printf("%d\n",i-1);

47             break;

48         }

49     }

50     return 0;

51 }