Find the number of ways to divide number into four parts such that a = c and b = d

Given a number N. Find the number of ways to divide a number into four parts(a, b, c, d) such that a = c and b = d and a not equal to b. 
Examples:

Input : N = 6 
Output : 1 
Explanation : four parts are {1, 2, 1, 2}
Input : N = 20 
Output : 4 
Explanation : possible ways are {1, 1, 9, 9}, {2, 2, 8, 8}, {3, 3, 7, 7} and {4, 4, 6, 6}.

Approach :
If the given N is odd the answer is 0, because the sum of four parts will not be even number.
If n is divisible by 4 then answer will be n/4 -1(here a equals to b can be possible so subtract that possibility) otherwise n/4.
Below is the implementation of the above approach : 

C++

// C++ implementation for above approach
#include <bits/stdc++.h>
using namespace std;

// Function to find the number of ways to divide
// N into four parts such that a = c and b = d
int possibleways(int n)
{
    if (n % 2 == 1)
        return 0;
    else if (n % 4 == 0)
        return n / 4 - 1;
    else
        return n / 4;
}

// Driver code
int main()
{
    int n = 20;
    cout << possibleways(n);
    return 0;
}

Java

// Java implementation for above approach
class GFG
{

// Function to find the number of ways to divide
// N into four parts such that a = c and b = d
static int possibleways(int n)
{
    if (n % 2 == 1)
        return 0;
    else if (n % 4 == 0)
        return n / 4 - 1;
    else
        return n / 4;
}

// Driver code
public static void main(String[] args)
{
    int n = 20;
    System.out.println(possibleways(n));
}
}

// This code contributed by Rajput-Ji

Python3

# Python3 implementation for above approach

# Function to find the number of ways
# to divide N into four parts
# such that a = c and b = d
def possibleways(n):

    if (n % 2 == 1):
        return 0;
    elif (n % 4 == 0):
        return n // 4 - 1;
    else:
        return n // 4;

# Driver code
n = 20;
print(possibleways(n));

# This code is contributed by mits

C#

// C# implementation for above approach
class GFG
{

// Function to find the number of ways to divide
// N into four parts such that a = c and b = d
static int possibleways(int n)
{
    if (n % 2 == 1)
        return 0;
    else if (n % 4 == 0)
        return n / 4 - 1;
    else
        return n / 4;
}

// Driver code
static void Main()
{
    int n = 20;
    System.Console.WriteLine(possibleways(n));
}
}

// This code is contributed by mits

PHP

<?php
// PHP implementation for above approach

// Function to find the number of ways to divide
// N into four parts such that a = c and b = d
function possibleways($n)
{
    if ($n % 2 == 1)
        return 0;
    else if ($n % 4 == 0)
        return $n / 4 - 1;
    else
        return $n / 4;
}

// Driver code
$n = 20;
echo possibleways($n);

// This code is contributed by ajit
?>

Javascript

<script>
// java script  implementation for above approach

// Function to find the number of ways to divide
// N into four parts such that a = c and b = d
function possibleways(n)
{
    if (n % 2 == 1)
        return 0;
    else if (n % 4 == 0)
        return n / 4 - 1;
    else
        return n / 4;
}

// Driver code
let n = 20;
document.write( possibleways(n));

// This code is contributed by Gottumukkala Bobby
</script>

Time Complexity: O(1)

Auxiliary Space: O(1)