Check if the game is valid or not

Three players P1, P2 and P3 are playing a game. But at a time only two players can play the game, so they decided, at a time two players will play the game and one will spectate. When one game ends, the one who lost the game becomes the spectator in the next game and the one who was spectating plays against the winner. There cannot be any draws in any game. Player P1 and P2 will play the first game. Input is the number of games played n and in next line winner of n games.

Examples :

Input : 
No. of Games : 4
Winner of the Game Gi : 1 1 2 3 
Output : YES
Explanation : 
Game1 : P1 vs P2 : P1 wins
Game2 : P1 vs P3 : P1 wins
Game3 : P1 vs P2 : P2 wins
Game4 : P3 vs P2 : P3 wins
None of the winners were invalid

Input : 
No. of Games : 2
Winner of the Game Gi : 2 1 
Output : NO
Explanation : 
Game1 : P1 vs P2 : P2 wins
Game2 : P2 vs P3 : P1 wins (Invalid winner)
In Game2 P1 is spectator 

Approach :
Start with P1 and P2 and continue the game while making the loser new spectator by subtracting the current spectator and winner from total sum of three players i.e. 6. An invalid entry will halt the process.

Below is the implementation for the above approach:

C++

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// CPP program to check if the game
// is valid
#include <bits/stdc++.h>
using namespace std;
  
string check_valid(int a[], int n)
{
    // starting with player P1 and P2 
    // so making P3 spectator
    int spec = 3;
    for (int i = 0; i < n; i++) {
      
        // If spectator wins a game 
        // then its not valid
        if (a[i] == spec) {
            return "Invalid";
        }
          
        // subtracting the current spectator 
        // and winner from total sum 6 which
        // makes losing player spectator
        spec = 6 - a[i] - spec;
    }
      
    // None of the winner is found spectator.
    return "Valid";
}
  
// Driver program to test above functions
int main()
{
    int n = 4;
    int a[n] = {1, 1, 2, 3};
    cout << check_valid(a, n);
    return 0;
}

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Java

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// java program to check if the game
// is valid
import java.io.*;
  
class GFG {
  
  
      
    static String check_valid(int a[], int n)
    {
        // starting with player P1 and P2 
        // so making P3 spectator
        int spec = 3;
          
        for (int i = 0; i < n; i++) {
          
            // If spectator wins a game 
            // then its not valid
            if (a[i] == spec) {
                return "Invalid";
            }
              
            // subtracting the current spectator 
            // and winner from total sum 6 which
            // makes losing player spectator
            spec = 6 - a[i] - spec;
        }
          
        // None of the winner is found spectator.
        return "Valid";
    }
      
    // Driver program to test above functions
    public static void main (String[] args) {
          
        int a[] = {1, 1, 2, 3};
        int n = a.length;
          
        System.out.println(check_valid(a, n));
      
        }
}
  
// This code is contributed by vt_m

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Python3

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# Python3 code to check if the game
# is valid
  
def check_valid( a , n ):
  
    # starting with player P1 and P2
    # so making P3 spectator
    spec = 3
    for i in range(n):
          
        # If spectator wins a game
        # then its not valid
        if a[i] == spec:
            return "Invalid"
          
        # subtracting the current spectator
        # and winner from total sum 6 which
        # makes losing player spectator
        spec = 6 - a[i] - spec
      
    # None of the winner is found spectator.
    return "Valid"
  
# Driver code to test above functions
n = 4
a = [1, 1, 2, 3]
print(check_valid(a, n))
  
# This code is contributed by "Sharad_Bhardwaj".

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C#

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// C# program to check if the game
// is valid
using System;
  
class GFG {
  
    static String check_valid(int []a, int n)
    {
        // starting with player P1 and P2 
        // so making P3 spectator
        int spec = 3;
          
        for (int i = 0; i < n; i++) {
          
            // If spectator wins a game 
            // then its not valid
            if (a[i] == spec) {
                return "Invalid";
            }
              
            // subtracting the current spectator 
            // and winner from total sum 6 which
            // makes losing player spectator
            spec = 6 - a[i] - spec;
        }
          
        // None of the winner is found spectator.
        return "Valid";
    }
      
    // Driver program 
    public static void Main () 
    {
        int []a = {1, 1, 2, 3};
        int n = a.Length;
          
        Console.WriteLine(check_valid(a, n));
      
        }
}
  
// This code is contributed by vt_m

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PHP

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<?php
// PHP program to check if 
// the game is valid
function check_valid( $a, $n)
{
    // starting with player P1 and P2 
    // so making P3 spectator
    $spec = 3;
    for ($i = 0; $i < $n; $i++) 
    {
      
        // If spectator wins a game 
        // then its not valid
        if ($a[$i] == $spec
        {
            return "Invalid";
        }
          
        // subtracting the current 
        // spectator and winner from 
        // total sum 6 which makes
        // losing player spectator
        $spec = 6 - $a[$i] - $spec;
    }
      
    // None of the winner is
    // found spectator.
    return "Valid";
}
  
// Driver Code
$n = 4;
$a = array(1, 1, 2, 3);
echo check_valid($a, $n); 
  
// This code is contributed by vt_m
?>

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Output :

Valid


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