贪心法讲解

 1 #include<iostream>
 2 #include<cstring>
 3 #include<cstdlib>
 4 #include<cstdio>
 5 #include<cmath>
 6 #include<algorithm>
 7 using namespace std;
 8 struct Sto {
 9     double Pri;
10     double Dist;
11 } Pot[9];
12 double Abt,v,Dist;
13 int n;
14 int main() {
15     scanf("%lf%lf%lf%lf%d",&Dist,&v,&Abt,&Pot[0].Pri,&n);
16     for(int i = 1; i<=n; i++) {
17         scanf("%lf%lf",&Pot[i].Dist,&Pot[i].Pri);
18     }
19     double Cost = 0,Now = 0;
20     int End = 0;
21     for(int i = 0; i<n; i++) {
22         if(Pot[i].Pri > Pot[i + 1].Pri) {
23             Cost += (Pot[i + 1].Dist - Now * Abt - Pot[i].Dist) * Pot[i].Pri / Abt;
24             End = i + 1;
25             Now = 0;
26         } else {
27             double Max = v * Abt;
28             if(Max < Pot[i + 1].Dist - Pot[End].Dist) {
29                 printf("-1");
30                 return 0;
31             } else {
32                 double Min = 1000;
33                 int Idx = 0;
34                 for(int j = i + 1; j<=n; j++) {
35                     if(Pot[j].Dist - Pot[End].Dist > Max) {
36                         break;
37                     }
38                     if(Pot[j].Pri <= Min) {
39                         Min = Pot[j].Pri;
40                         Idx = j;
41                         if(Min <= Pot[End].Pri) {
42                             break;
43                         }
44                     }
45                 }
46                 if(Min > Pot[End].Pri) {
47                     Cost += (v - Now) * Pot[End].Pri;
48                     Now = v - (Pot[Idx].Dist - Pot[End].Dist) / Abt;
49                     if(Now * Abt >= Dist - Pot[Idx].Dist) {
50                         Cost -= (Now * Abt - Dist + Pot[Idx].Dist) * Pot[End].Pri / Abt;
51                         printf("%.2lf",Cost);
52                         return 0;
53                     }
54                 } else {
55                     Cost += (Pot[Idx].Dist - Now * Abt - Pot[End].Dist) * Pot[End].Pri / Abt;
56                     Now = 0;
57                 }
58                 i = Idx - 1;
59                 End = Idx;
60             }
61         }
62     }
63     Cost += max(0.0,(Dist - Pot[End].Dist - Now * Abt) * Pot[End].Pri / Abt);        //可以不用max了，我前面已经return0了 
64     printf("%.2lf",Cost);
65     return 0;
66 }