Problem:
Score : 300 points

Problem Statement

Given is a sequence of integers A_1, A_2, ..., A_N.
If its elements are pairwise distinct, print YES; otherwise, print NO.

Constraints

2 ≤ N ≤ 200000

1 ≤ A_i ≤ 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 ... A_N

Output

If the elements of the sequence are pairwise distinct, print YES; otherwise, print NO.

Sample Input 1

5
2 6 1 4 5

Sample Output 1

YES

The elements are pairwise distinct.

Sample Input 2

6
4 1 3 1 6 2

Sample Output 2

NO

The second and fourth elements are identical.

Sample Input 3

2
10000000 10000000

Sample Output 3

NO

Solution in C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
int main(void){
    int N;
    scanf("%d",&N);
    int *a;
    a = (int*)malloc(sizeof(int)*N);//動的確保
    for(int i=0;i<N;i++){
    scanf("%d",&a[i]);
    }
    int checknum1=0;
    int checknum2=0;
    int flag = 0;
    for(int i=0;i<N;i++){
        checknum1 = a[i];
        checknum2 = a[N-i];
        /*for(int j=0;j<N;j++){
            if(checknum1==a[j]&&i!=j){
                flag = 1;
            }
            if(checknum2==a[j]&&(N-i)!=j){
                flag = 1;
            }
        }*/
        if(checknum1==checknum2){
            flag=1;
        }
    }

    if(flag){
        printf("NO");
    }else{
        printf("YES");
    }
    return 0;
}