POJ-2355 Railway tickets DP优化

　　题目链接：http://poj.org/problem?id=2355

　　简单的DP，转移方程：f[i][j]=Min { f[i][k] + C(n) }，注意到f[i][j]是单调递增的，用二分搜索优化即可。注意到此题有个trick，那就是s>e!!!

 1 //STATUS:C++_AC_16MS_252KB

 2 #include<stdio.h>

 3 #include<stdlib.h>

 4 #include<string.h>

 5 #include<math.h>

 6 #include<iostream>

 7 #include<string>

 8 #include<algorithm>

 9 #include<vector>

10 #include<queue>

11 #include<stack>

12 #include<map>

13 using namespace std;

14 #define LL __int64

15 #define pii pair<int,int>

16 #define Max(a,b) ((a)>(b)?(a):(b))

17 #define Min(a,b) ((a)<(b)?(a):(b))

18 #define mem(a,b) memset(a,b,sizeof(a))

19 #define lson l,mid,rt<<1

20 #define rson mid+1,r,rt<<1|1

21 const int N=10010,INF=0x3f3f3f3f,MOD=1000000007;

22 const double DNF=100000000000;

23 

24 int d[N];

25 LL f[N];

26 int l1,l2,l3,c1,c2,c3,n,s,e;

27 

28 LL binary(int low,int i,int cost)

29 {

30     int l=s,r=i,mid;

31     while(l<r)

32     {

33         mid=(l+r)>>1;

34         if(d[mid]>=low)r=mid;

35         else l=mid+1;

36     }

37     return f[l]+cost;

38 }

39 

40 int main()

41 {

42  //   freopen("in.txt","r",stdin);

43     int i,j,t;

44     while(~scanf("%d%d%d%d%d%d",&l1,&l2,&l3,&c1,&c2,&c3))

45     {

46         mem(f,INF);

47         scanf("%d%d%d",&n,&s,&e);

48         for(i=2;i<=n;i++)

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

50         if(s>e)t=s,s=e,e=t;

51 

52         f[s]=0;

53         for(i=s+1;i<=e;i++){

54             t=d[i]-l1;

55             f[i]=Min(f[i],binary(t,i,c1));

56             t=d[i]-l2;

57             f[i]=Min(f[i],binary(t,i,c2));

58             t=d[i]-l3;

59             f[i]=Min(f[i],binary(t,i,c3));

60         }

61 

62         printf("%I64d\n",f[e]);

63     }

64     return 0;

65 }