1 #include <iostream> 2 #include <algorithm> 3 #include <vector> 4 5 using namespace std; 6 7 int check(int a, int b){ 8 if(a - b > 0 )return 1; 9 else if(a-b < 0) return -1; 10 else return 0; 11 } 12 13 int main(){ 14 int n; 15 cin >> n; 16 vector<int> x(n); 17 for(int i = 0; i < n; ++ i) cin >> x[i]; 18 int i; 19 for( i = 3; i < n ; ++ i){ 20 int j ; 21 for(j = 0 ; j < i-1; j ++){ 22 int a = check(x[j],x[i-1]); 23 int b = check(x[j],x[i]); 24 int c = check(x[j+1],x[i-1]); 25 int d = check(x[j+1],x[i]); 26 if(a*b*c*d < 0){ 27 cout<<"yes"<<endl; 28 break; 29 } 30 } 31 if(j < i-1) break; 32 } 33 if(i >= n) cout<<"no"<<endl; 34 }