题目：https://www.lydsy.com/JudgeOnline/problem.php?id=1597
就是斜率优化水题...
然而WA了十几遍，正负号处理真让人心累...
还是该负就负，别乱换了...
代码如下：
#include<iostream> #include<cstdio> #include<cstring> #include<algorithm> using namespace std; typedef long long ll; int const maxn=50005; int n,cnt,q[maxn],h,t; ll f[maxn],x[maxn],y[maxn]; struct N{ll a,b;}p[maxn]; ll rd() { ll ret=0,f=1;char ch=getchar(); while(ch<'0'||ch>'9'){if(ch=='-')f=-1; ch=getchar();} while(ch>='0'&&ch<='9')ret=ret*10+ch-'0',ch=getchar(); return ret*f; } //bool cmp(N x,N y){return x.a==y.a?x.b>y.b:x.a<y.a;} bool cmp(N x,N y){return x.a==y.a?x.b>y.b:x.a<y.a;} double slp(int a,int b){return (double)(f[b]-f[a])/(double)(y[a+1]-y[b+1]);} int main() { n=rd(); for(int i=1;i<=n;i++)p[i].a=rd(),p[i].b=rd(); sort(p+1,p+n+1,cmp); for(int i=1;i<=n;i++) { // if(p[i].a==p[i-1].a)continue; // x[++cnt]=p[i].a; y[cnt]=p[i].b; while (cnt && p[i].b>=y[cnt]) cnt--; x[++cnt]=p[i].a; y[cnt]=p[i].b; } // h=1;t=1;// for(int i=1;i<=cnt;i++) { while(h<t&&slp(q[h],q[h+1])<x[i])h++;//< f[i]=f[q[h]]+x[i]*y[q[h]+1]; while(h<t&&slp(q[t-1],q[t])>slp(q[t],i))t--; q[++t]=i; } printf("%lld",f[cnt]); return 0; }