# Check if it is possible to serve customer queue with different notes

Given cost of the ticket ’25’ and an integer array ‘arr’ which holds the values of the notes people in a queue are having (either ’25’, ’50’ or ‘100’ Rs. Notes).
The task is to find whether it possible to sell tickets to the people in order, starting from 0 Rs.

Examples:

```Input: arr = {25, 25, 50, 50}
Output: YES
You can give the 25 you received from the 1st customer
to the 3rd customer and then the 25 from the 2nd customer to the 4th.

Input: arr = {25, 100}
Output: NO
It is not possible to return the change to the 2nd customer.
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: Keep a track of the number of Rs. 25 and Rs. 50 notes that we currently have as ‘c25’ and ‘c50’ respectively. There is no need to keep track of the number of Rs. 100 notes as we can not return them to any customer. There are 3 possibilities now:

• If the customer pays Rs. 25 : Increment c25, nothing has to be returned to the customer.
• If the customer pays Rs. 50 : Rs. 25 has to be returned to the customer, check if `c25>0` then increment c50 and decrement c25.
• If the customer pays Rs. 100 : Rs. 75 has to be returned to the customer. There are two ways to do it, either using one Rs. 50 and one Rs. 25 note or using three Rs. 25 notes. We’ll prefer the first way so that if in future someone with Rs. 50 comes, we’ll still have our 25s left with us. Check whether it is possible and decrement the counts accordingly.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function that returns ` `// true is selling of ` `// the tickets is possible ` `bool` `isSellingPossible(``int` `n, ``int` `a[]) ` `{ ` `    ``int` `i, c25 = 0, c50 = 0; ` `    ``for` `(i = 0; i < n; i++) { ` ` `  `        ``// Nothing to return ` `        ``// to the customer ` `        ``if` `(a[i] == 25) ` `            ``c25++; ` `        ``else` `if` `(a[i] == 50) { ` `            ``c50++; ` ` `  `            ``// Check if 25 can be ` `            ``// returned to customer. ` `            ``if` `(c25 == 0) ` `                ``break``; ` `            ``c25--; ` `        ``} ` `        ``else` `{ ` ` `  `            ``// Try returning one ` `            ``// 50 and one 25 ` `            ``if` `(c50 > 0 && c25 > 0) { ` `                ``c50--; ` `                ``c25--; ` `            ``} ` ` `  `            ``// Try returning three 25 ` `            ``else` `if` `(c25 >= 3) ` `                ``c25 -= 3; ` `            ``else` `                ``break``; ` `        ``} ` `    ``} ` ` `  `    ``// If the loop did not break, ` `    ``// all the tickets were sold ` `    ``if` `(i == n) ` `        ``return` `true``; ` `    ``else` `        ``return` `false``; ` `} ` ` `  `// Driver Program to ` `// test above function ` `int` `main() ` `{ ` `    ``int` `a[] = { 25, 25, 50, 100 }; ` `    ``int` `n = ``sizeof``(a) / ``sizeof``(a); ` ` `  `    ``if` `(isSellingPossible(n, a)) { ` `        ``cout << ``"YES"``; ` `    ``} ` `    ``else` `{ ` `        ``cout << ``"NO"``; ` `    ``} ` `} `

## Java

 `// Java implementation of the approach ` `class` `GFG ` `{ ` `// Function that returns ` `// true is selling of ` `// the tickets is possible ` `static` `boolean` `isSellingPossible(``int` `n, ` `                                 ``int` `a[]) ` `{ ` `    ``int` `i, c25 = ``0``, c50 = ``0``; ` `    ``for` `(i = ``0``; i < n; i++) ` `    ``{ ` ` `  `        ``// Nothing to return ` `        ``// to the customer ` `        ``if` `(a[i] == ``25``) ` `            ``c25++; ` `        ``else` `if` `(a[i] == ``50``) ` `        ``{ ` `            ``c50++; ` ` `  `            ``// Check if 25 can be ` `            ``// returned to customer. ` `            ``if` `(c25 == ``0``) ` `                ``break``; ` `            ``c25--; ` `        ``} ` `        ``else` `        ``{ ` ` `  `            ``// Try returning one ` `            ``// 50 and one 25 ` `            ``if` `(c50 > ``0` `&& c25 > ``0``)  ` `            ``{ ` `                ``c50--; ` `                ``c25--; ` `            ``} ` ` `  `            ``// Try returning three 25 ` `            ``else` `if` `(c25 >= ``3``) ` `                ``c25 -= ``3``; ` `            ``else` `                ``break``; ` `        ``} ` `    ``} ` ` `  `    ``// If the loop did not break, ` `    ``// all the tickets were sold ` `    ``if` `(i == n) ` `        ``return` `true``; ` `    ``else` `        ``return` `false``; ` `} ` ` `  `// Driver Code ` `public` `static` `void` `main(String []args) ` `{ ` `    ``int` `a[] = { ``25``, ``25``, ``50``, ``100` `}; ` `    ``int` `n = a.length; ` ` `  `    ``if` `(isSellingPossible(n, a))  ` `    ``{ ` `        ``System.out.println(``"YES"``); ` `    ``} ` `    ``else`  `    ``{ ` `        ``System.out.println(``"NO"``); ` `    ``} ` `} ` `} ` ` `  `// This code is contributed ` `// by ihritik `

## Python3

 `# Python3 implementation of the approach ` ` `  `# Function that returns true is selling ` `# of the tickets is possible ` `def` `isSellingPossible(n, a): ` ` `  `    ``c25 ``=` `0``; ` `    ``c50 ``=` `0``; ` `    ``i ``=` `0``; ` `    ``while``(i < n):  ` `     `  ` `  `        ``# Nothing to return to the customer ` `        ``if` `(a[i] ``=``=` `25``): ` `            ``c25 ``+``=` `1``; ` `        ``elif` `(a[i] ``=``=` `50``):  ` `         `  `            ``c50 ``+``=` `1``; ` ` `  `            ``# Check if 25 can be returned  ` `            ``# to customer. ` `            ``if` `(c25 ``=``=` `0``): ` `                ``break``; ` `            ``c25 ``-``=` `1``; ` `         `  `        ``else``: ` `     `  `            ``# Try returning one ` `            ``# 50 and one 25 ` `            ``if` `(c50 > ``0` `and` `c25 > ``0``): ` `             `  `                ``c50 ``-``=` `1``; ` `                ``c25 ``-``=` `1``; ` `             `  `            ``# Try returning three 25 ` `            ``elif` `(c25 >``=` `3``): ` `                ``c25 ``-``=` `3``; ` `            ``else``: ` `                ``break``; ` `        ``i ``+``=` `1``; ` `     `  `    ``# If the loop did not break, ` `    ``# all the tickets were sold ` `    ``if` `(i ``=``=` `n): ` `        ``return` `True``; ` `    ``else``: ` `        ``return` `False``; ` ` `  `# Driver Code ` `a ``=` `[ ``25``, ``25``, ``50``, ``100` `]; ` `n ``=` `len``(a); ` ` `  `if` `(isSellingPossible(n, a)): ` `    ``print``(``"YES"``); ` `else``: ` `    ``print``(``"NO"``); ` ` `  `# This code is contributed by mits `

## C#

 `// C# implementation of the approach ` `using` `System; ` ` `  `class` `GFG ` `{ ` `// Function that returns ` `// true is selling of ` `// the tickets is possible ` `static` `bool` `isSellingPossible(``int` `n, ``int` `[]a) ` `{ ` `    ``int` `i, c25 = 0, c50 = 0; ` `    ``for` `(i = 0; i < n; i++)  ` `    ``{ ` ` `  `        ``// Nothing to return ` `        ``// to the customer ` `        ``if` `(a[i] == 25) ` `            ``c25++; ` `        ``else` `if` `(a[i] == 50) ` `        ``{ ` `            ``c50++; ` ` `  `            ``// Check if 25 can be ` `            ``// returned to customer. ` `            ``if` `(c25 == 0) ` `                ``break``; ` `            ``c25--; ` `        ``} ` `        ``else`  `        ``{ ` ` `  `            ``// Try returning one ` `            ``// 50 and one 25 ` `            ``if` `(c50 > 0 && c25 > 0) ` `            ``{ ` `                ``c50--; ` `                ``c25--; ` `            ``} ` ` `  `            ``// Try returning three 25 ` `            ``else` `if` `(c25 >= 3) ` `                ``c25 -= 3; ` `            ``else` `                ``break``; ` `        ``} ` `    ``} ` ` `  `    ``// If the loop did not break, ` `    ``// all the tickets were sold ` `    ``if` `(i == n) ` `        ``return` `true``; ` `    ``else` `        ``return` `false``; ` `} ` ` `  `// Driver Code ` `public` `static` `void` `Main() ` `{ ` `    ``int` `[]a = { 25, 25, 50, 100 }; ` `    ``int` `n = a.Length; ` ` `  `    ``if` `(isSellingPossible(n, a)) ` `    ``{ ` `        ``Console.WriteLine(``"YES"``); ` `    ``} ` `    ``else`  `    ``{ ` `        ``Console.WriteLine(``"NO"``); ` `    ``} ` `} ` `} ` ` `  `// This code is contributed ` `// by ihritik `

## PHP

 ` 0 && ``\$c25` `> 0) ` `            ``{ ` `                ``\$c50``--; ` `                ``\$c25``--; ` `            ``} ` ` `  `            ``// Try returning three 25 ` `            ``else` `if` `(``\$c25` `>= 3) ` `                ``\$c25` `-= 3; ` `            ``else` `                ``break``; ` `        ``} ` `    ``} ` ` `  `    ``// If the loop did not break, ` `    ``// all the tickets were sold ` `    ``if` `(``\$i` `== ``\$n``) ` `        ``return` `true; ` `    ``else` `        ``return` `false; ` `} ` ` `  `// Driver Code ` `\$a` `= ``array``( 25, 25, 50, 100 ); ` `\$n` `= sizeof(``\$a``); ` ` `  `if` `(isSellingPossible(``\$n``, ``\$a``)) ` `{ ` `    ``echo` `"YES"``; ` `} ` `else` `{ ` `    ``echo` `"NO"``; ` `} ` ` `  `// This code is contributed ` `// by ihritik ` `?> `

Output:

```YES
```

Time Complexity: O(N)

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