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 <stdlib.h>
#include <string.h>
#define SENTINEL 1000000000
int main(void){
int n,A[200005];
int count;
int flag=0;
int count2;
int count3;
int i;
scanf("%d",&n);
for(count=0;count<n;count++){
scanf("%d",&A[count]);
}
  mergeSort(A,0,n);
 
for(count=0;count<n;count++){
if(A[count]==A[count+1]){printf("NO"); return 0;}
}
 printf("YES");
  
}
 
 
 
 
 
void mergeSort(int A[],int left,int right){
  int i,mid;
  if(left+1<right){
    mid=(left+right)/2;
    mergeSort(A,left,mid);
    mergeSort(A,mid,right);
    merge(A,left,mid,right);
  }
}
 
 
 
void merge(int A[],int left,int mid,int right){
    int count;
  int n1,n2,i,j,k;
  int *L,*R;
  n1=mid-left;
  n2=right-mid;
  L=(int *)malloc(sizeof(int)*(n1+1));
  R=(int *)malloc(sizeof(int)*(n2+1));
  for(i=0;i<=n1-1;i++){
    L[i]=A[left+i];
  }
  for(j=0;j<=n2-1;j++){
    R[j]=A[mid+j];
  }
  L[n1]=SENTINEL;
  R[n2]=SENTINEL;
  i=0;
  j=0;
  for(k=left;k<=right-1;k++){
   if(L[i]<=R[j]){
      A[k]=L[i];
      i++;
      count++;
    }
    else{
      A[k]=R[j];
      j++;
      count++;
    }
  }
  free(L);
  free(R);
}