Codeforces Round #208 (Div. 2) A.Dima and Continuous Line

 #include <iostream>
 #include <algorithm>
 #include <vector>

 using namespace std;

 int check(int a, int b){
     if(a - b >  )return ;
     else if(a-b < ) return -;
     else return ;
 }

 int main(){
     int n;
     cin >> n;
     vector<int> x(n);
     for(int i = ; i < n; ++ i) cin >> x[i];
     int i;
     for( i = ; i < n ; ++ i){
         int j ;
         for(j =  ; j < i-; j ++){
             int a = check(x[j],x[i-]);
             int b = check(x[j],x[i]);
             int c = check(x[j+],x[i-]);
             int d = check(x[j+],x[i]);
             if(a*b*c*d < ){
                 cout<<"yes"<<endl;
                 break;
             }
         }
         if(j < i-) break;
     }
     if(i >= n) cout<<"no"<<endl;
 }