hdu3507 斜率优化dp

//直接比较斜率容易出问题，因为是浮点型，wa了很多次#include<iostream>#include<cstdio>#include<cmath>#define N 500010using namespace std;int a[N],s[N],dp[N],id[N];int n,m;int up(int i,int j){    return dp[i]-dp[j]+s[i]*s[i]-s[j]*s[j];}int down(int i,int j){     return 2*(s[i]-s[j]);}int get(int x,int i){ return dp[x]+(s[i]-s[x])*(s[i]-s[x])+m;}int main(){    //freopen("1.in","r",stdin);     while(scanf("%d%d",&n,&m)!=EOF)     {                   s[0]=0;                   for(int i=1;i<=n;i++){scanf("%d",&a[i]);s[i]=s[i-1]+a[i];}                   int head=0,tail=1;id[0]=0;dp[0]=0;                   for(int i=1;i<=n;i++)                   {                            while(head<tail-1&&up(id[head+1],id[head])<=s[i]*down(id[head+1],id[head]))head++;                            dp[i]=get(id[head],i);                            while(head<tail-1&&up(i,id[tail-1])*down(id[tail-1],id[tail-2])<=up(id[tail-1],id[tail-2])*down(i,id[tail-1]))tail--;                            id[tail++]=i;                   }                   printf("%d\n",dp[n]);     }     return 0;}