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: Accepted)

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

int low[200000];
int high[200000];
int a[200000];

int part(int a[],int l,int r){
  int i,j,x,t;

  i = l - 1;
  j = r;

  x = a[r];

  while(1){
    while(a[++i] < x);
    while(i < --j && x < a[j]);

    if(i >= j) break;

    t = a[i]; a[i] = a[j]; a[j] = t;
  }

  t = a[i]; a[i] = a[r]; a[r] = t;
  return i;
}

void quicksort(int a[],int n){
  int l,r,v;
  int sp;

  low[0] = 0;
  high[0] = n - 1;
  sp = 1;

  while(sp > 0){
    sp--;
    l = low[sp];
    r = high[sp];

    if(l >= r);

    else {
      v = part(a,l,r);

      if(v - l < r - v){
        low[sp] = v + 1;
        high[sp++] = r;
        low[sp] = l;
        high[sp++] = v - 1;
      }

      else{
        low[sp] = l;
        high[sp++] = v - 1;
        low[sp] = v + 1;
        high[sp++] = r;
      }
    }
  }
}

int main(){
  int n,i;
  int flag = 0;

  scanf("%d", &n);

  for(i = 0;i < n;i++) scanf("%d", &a[i]);

  quicksort(a,n);

  for(i = 0;i < n - 1;i++){
    if(a[i] == a[i + 1]){
      printf("NO\n");
      flag = 1;
      break;
    }
  }

  if(flag == 0) printf("YES\n");

  return 0;
}