USACO3.15stamps（dp）

对dp很无奈。。枚举所有可能达到的值 dp[i]表示到达i值所用最少的邮票 

 1 /*

 2     ID: shangca2

 3     LANG: C++

 4     TASK: stamps

 5 */

 6 #include <iostream>

 7 #include<cstdio>

 8 #include<cstring>

 9 #include<stdlib.h>

10 #include<algorithm>

11 using namespace std;

12 int p[55],dp[2000010];

13 bool o[2000010];

14 int main()

15 {

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

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

18     int i,j,k,n;

19     cin>>n>>k;

20     for(i = 1 ; i <= k ; i++)

21     {

22         cin>>p[i];

23         o[p[i]] = 1;

24         dp[p[i]] = 1;

25     }

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

27     {

28         if(o[i]&&dp[i]<n)

29         {

30             for(j = 1 ; j <= k ;j++)

31             {

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

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

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

35                 else

36                 dp[i+p[j]] = min(dp[i]+1,dp[i+p[j]]);

37             }

38         }

39         else if(!o[i])

40         {

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

42             break;

43         }

44     }

45     return 0;

46 }

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