JZYZOJ1330 土地购买 dp 斜率优化

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 #include<iostream>
 5 #include<cmath>
 6 using namespace std;
 7 int n;
 8 struct wtff{
 9     long long x;
10     long long y;
11 }wtf[50010];
12 long long x[50010]={},y[50010]={};
13 long long f[50010]={};
14 long long q[50010]={};
15 int head=0,tail=0;
16 bool mycmp(wtff a,wtff b){
17     return (a.x<b.x||
18     (a.x==b.x&&a.y<b.y));
19 }
20 inline double www(int a,int b){
21     return ((double)(f[a]-f[b])/(y[b+1]-y[a+1]));
22 }
23 int main(){
24     scanf("%d",&n);
25     for(int i=1;i<=n;i++){
26         scanf("%d%d",&wtf[i].x,&wtf[i].y);
27     }
28     sort(wtf+1,wtf+1+n,mycmp);
29     int en=0;
30     int bign=-100;
31     for(int i=n;i>=1;i--){
32         if(wtf[i].y>bign){
33             if(wtf[i].x!=x[en]){
34                 x[++en]=wtf[i].x;
35                 y[en]=wtf[i].y;
36             }
37             else{
38                 x[en]=wtf[i].x;
39                 y[en]=wtf[i].y;
40             }
41             bign=wtf[i].y;
42         }
43     }
44     for(int i=1;i<=en/2;i++){
45         swap(x[i],x[en+1-i]);
46         swap(y[i],y[en+1-i]);
47     }
48     for(int i=1;i<=en;i++){
49         while(head<tail&&www(q[head+1],q[head])<x[i]){
50             head++;
51         }
52         int j=q[head];
53         f[i]=f[j]+x[i]*y[j+1];
54         while(head<tail&&www(i,q[tail])<www(q[tail],q[tail-1])){
55             tail--;
56         }
57         q[++tail]=i;
58     }
59     cout<<f[en]<<endl;
60     return 0;
61 }