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# (Mono 4.6.2.0) (judge verdict: Accepted)

/*********************************************
* 20.05.18 AtCoder Beginner Contest 154. 
* 
*
*********************************************/
/*********************************************
::test input::
*********************************************/

namespace TempName{
    using System;
    using System.Linq;
    using System.Collections.Generic;
    using System.Reflection;
    using System.Text;
    using static System.Console;
    using static IOmacro.CSharpInput; 
    using static IOmacro.CppInput;
    using static IOmacro.CConst;

    public class CRun{
        public readonly char problem_num = 'C';
        
        public void solve_1() {
            // A - Remaining Balls 
            // 문자열 S가 쓰인 공이 A개, 문자열 T인 공이 B개
            // 문자열 U가 쓰인 공을 1개 골라서 버림
            // 문자열 S, T가 써져있는 공이 남은 수는?
            
            string S = cin;
            string T = cin;
            int A = cin;
            int B = cin;
            string U = _string;
            
            A -= (S == U ? 1 : 0);
            B -= (T == U ? 1 : 0);
            WriteLine($"{A} {B}");
        }

        public void solve_2() {
            // B - I miss you... 
            // 주어진 문자열의 모든 문자를 x로 치환하시오
            
            string input = _string;
            int slen = input.Length;
            var ans = new StringBuilder();
            for (int i = 0; i < slen; i++) {
                ans.Append("x");
            }
            
            WriteLine(ans);
        }

        public void solve_3() {
            // C - Distinct or Not 
            // 정수열 A1..AN이 모두 다른 정수인지 판단
            // N = 200000
            
            int N = _int;
            string[] A = _stringa;
            
            string ans = "YES";
            var hash = new HashSet<string>();
            
            foreach (var ix in A) {
                if (!hash.Add(ix)) {
                    ans = "NO";
                    break;
                }
            }
            
            WriteLine(ans);
        }
        
        public void solve_4() {
            
        }
        
        public void solve_5() {
            
        }
        
        public void solve_6() {
            
        }
    }
    
    class Program { 
        static void Main() { 
            var run = new CRun();
            if (run.problem_num == 'A') run.solve_1(); 
            if (run.problem_num == 'B') run.solve_2(); 
            if (run.problem_num == 'C') run.solve_3();
            if (run.problem_num == 'D') run.solve_4();
            if (run.problem_num == 'E') run.solve_5();
            if (run.problem_num == 'F') run.solve_6();
        } 
    }
}

namespace IOmacro {
    //20.05.10. 수정
    
    using System; 
    using System.Linq; 
    using System.IO;
    using System.Collections.Generic;
    
    public class CSharpInput {
        public static StreamWriter _writer = new StreamWriter(Console.OpenStandardOutput());
        public const char separator = ' ';
        public static string _string{get{return Console.ReadLine();}}
        public static string[] _stringa{get{return (Console.ReadLine().Split(separator));}}
        public static int _int{get{return int.Parse(Console.ReadLine());}}
        public static int[] _inta{get{return Console.ReadLine().Split(separator).Select(int.Parse).ToArray();}}
        public static long _long{get{return long.Parse(Console.ReadLine());}}
        public static long[] _longa{get{return Console.ReadLine().Split(separator).Select(long.Parse).ToArray();}}    
        public static double _double{get{return double.Parse(Console.ReadLine());}}
        public static double[] _doublea{get{return Console.ReadLine().Split(separator).Select(double.Parse).ToArray();}}    
    }
    
    public class CConst {
        public static readonly int MINI = int.MaxValue;
        public static readonly long INF = Int64.MaxValue;
    }
    
    public class CppInput {
        public static CppInput cin => new CppInput();
        public const char separator = ' ';
        private static readonly Queue<string> _input = new Queue<string>();
        private CppInput(){}
        public static implicit operator string(CppInput _) {
            if (_input.Count == 0) Console.ReadLine().Split(separator).foreachExtension(x => _input.Enqueue(x));
            return _input.Dequeue();
        }
        public static implicit operator int(CppInput _){
            if (_input.Count == 0) Console.ReadLine().Split(separator).foreachExtension(x => _input.Enqueue(x));
            return int.Parse(_input.Dequeue());
        }
        public static implicit operator long(CppInput _){
            if (_input.Count == 0) Console.ReadLine().Split(separator).foreachExtension(x => _input.Enqueue(x));
            return long.Parse(_input.Dequeue());
        }
        public static implicit operator double(CppInput _){
            if (_input.Count == 0) Console.ReadLine().Split(separator).foreachExtension(x => _input.Enqueue(x));
            return double.Parse(_input.Dequeue());
        }
    }
    
    public static class EnumerableExtension {
        public delegate void Function<in T>(T val);
        public static void foreachExtension<T>(this IEnumerable<T> enumerable, Function<T> function) {
            foreach (var x in enumerable) function(x);
        }
    }
}