CodeForces - 849B 几何

#include<stdio.h>
#include<set>
#include<algorithm>
using namespace std;

int a[1010],n;
set<double>s;

bool judge(double k)
{
    s.clear();
    for(int i=1; i<=n; ++i)
        s.insert(a[i]*1.0-k*i);
    return s.size()==2;
}

int main()
{
    scanf("%d",&n);
    for(int i=1; i<=n; ++i)
        scanf("%d",&a[i]);
    if(judge((a[2]-a[1])/1.0)||judge((a[3]-a[2])/1.0)||judge((a[3]-a[1])/2.0))
        printf("Yes\n");
    else
        printf("No\n");
    return 0;
}