Check if a given array can be divided into pairs with even sum

13 Sep, 2021
Given an array arr[] consisting of N integers, the task is to check if it is possible to divide the entire array into pairs such that the sum of each pair is even. If it is possible, print “Yes”. Otherwise, print “No”.
Examples:
Input: arr[] = {3, 2, 1, 4, 7, 5, }Output: YesExplanation:The given array can be divided into pairs: {1, 3}, {2, 4}, {5, 7}.
Input: arr[] = {1, 2, 3, 4, 5, 6}Output: NoExplanation:No possible pair distribution exists such that each pair sum is even.
Naive Approach: The simplest approach to solve the problem is to traverse the given array and for each element, find an element having the same parity which has not been picked yet and mark both the elements picked to avoid repetitions. If for any element, no suitable element is found, print “No”. Otherwise, if the entire array could be partitioned into desired pairs, print “Yes”. 
Time Complexity: O(N2)Auxiliary Space: O(N)
Efficient Approach: The idea is to observe the fact that if the count of even and odd numbers present in the given array are both even, only then, the given array can be divided into pairs having even sum by odd numbers together and even numbers together. Follow the steps below to solve the problem:
Find the total number of odd and even elements present in the given array and store it in two variables, countEven and countOdd respectively.Check if both countEven and countOdd are even or not. If found to be true, print “Yes”.Otherwise, print “No”.
Find the total number of odd and even elements present in the given array and store it in two variables, countEven and countOdd respectively.
Check if both countEven and countOdd are even or not. If found to be true, print “Yes”.
Otherwise, print “No”.
Below is the implementation of the above approach:
C++
Java
Python3
C#
Javascript
// C++ program for the above approach #include <bits/stdc++.h>using namespace std; // Function to check if we can split// array into pairs of even sum or notbool canPairs(int arr[], int n){    // If the length is odd then it    // is not possible to make pairs    if (n % 2 == 1)        return false;     // Initialize count of odd & even    int odd_count = 0, even_count = 0;     // Iterate through the array    for (int i = 0; i < n; i++)    {        // Count even element        if (arr[i] % 2 == 0)            even_count++;        else            odd_count++;    }     // If count of even elements    // and odd elements are even    if (even_count % 2 == 0 && odd_count % 2 == 0)    {        return true;    }     return false;} // Driver Codeint main(){    int arr[] = { 3, 2, 1, 4, 7, 5 };     int N = sizeof(arr) / sizeof(arr[0]);     // Function Call    if (canPairs(arr, N)) {        cout << "Yes";    }    else {        cout << "No";    }     return 0;}
// Java program for the above approachimport java.io.*; class GFG {     // Function to check if we can split    // array into pairs of even sum or not    static boolean canPairs(int[] arr, int n)    {        // If the length is odd then it        // is not possible to make pairs        if (n % 2 == 1)            return false;         // Initialize count of odd & even        int odd_count = 0, even_count = 0;         // Iterate through the array        for (int i = 0; i < n; i++)        {            // Count even element            if (arr[i] % 2 == 0)                even_count++;            else                odd_count++;        }         // If count of even elements        // and odd elements are even        if (even_count % 2 == 0 && odd_count % 2 == 0)        {            return true;        }        return false;    }     // Driver Code    public static void main(String[] args)    {        int[] arr = { 3, 2, 1, 4, 7, 5 };        int N = arr.length;         // Function call        if (canPairs(arr, N))            System.out.println("Yes");        else            System.out.println("No");    }} // This code is contributed by akhilsaini
# Python3 program for the above approach # Function to check if we can split# array into pairs of even sum or not  def canPairs(arr, n):     # If the length is odd then it    # is not possible to make pairs    if (n % 2 == 1):        return False     # Initialize count of odd & even    odd_count = 0    even_count = 0     # Iterate through the array    for i in range(0, n):         # Count even element        if (arr[i] % 2 == 0):            even_count = even_count + 1        else:            odd_count = odd_count + 1     # If count of even elements    # and odd elements are even    if ((even_count % 2 == 0) and            (odd_count % 2 == 0)):        return True     return False  # Driver Codeif __name__ == '__main__':     arr = [3, 2, 1, 4, 7, 5]    N = len(arr)     # Function call    if (canPairs(arr, N)):        print("Yes")    else:        print("No") # This code is contributed by akhilsaini
// C# program for the above approachusing System; class GFG {     // Function to check if we can split    // array into pairs of even sum or not    static bool canPairs(int[] arr, int n)    {         // If the length is odd then it        // is not possible to make pairs        if (n % 2 == 1)            return false;         // Initialize count of odd & even        int odd_count = 0, even_count = 0;         // Iterate through the array        for (int i = 0; i < n; i++)        {            // Count even element            if (arr[i] % 2 == 0)                even_count++;            else                odd_count++;        }         // If count of even elements        // and odd elements are even        if (even_count % 2 == 0 && odd_count % 2 == 0)        {            return true;        }        return false;    }     // Driver Code    public static void Main()    {        int[] arr = { 3, 2, 1, 4, 7, 5 };        int N = arr.Length;         // Function call        if (canPairs(arr, N))            Console.Write("Yes");        else            Console.Write("No");    }} // This code is contributed by akhilsaini
<script> // Javascript program for the above approach // Function to check if we can split// array into pairs of even sum or notfunction canPairs(arr, n){         // If the length is odd then it    // is not possible to make pairs    if (n % 2 == 1)        return false;     // Initialize count of odd & even    let odd_count = 0, even_count = 0;     // Iterate through the array    for(let i = 0; i < n; i++)    {                 // Count even element        if (arr[i] % 2 == 0)            even_count++;        else            odd_count++;    }     // If count of even elements    // and odd elements are even    if (even_count % 2 == 0 &&         odd_count % 2 == 0)    {        return true;    }    return false;} // Driver Codelet arr = [ 3, 2, 1, 4, 7, 5 ];let N = arr.length; // Function callif (canPairs(arr, N))    document.write("Yes");else    document.write("No");     // This code is contributed by target_2   </script>
Yes
Time Complexity: O(N)Auxiliary Space: O(1)
akhilsaini
ArifShaikh
target_2
khushboogoyal499
divisibility
Arrays
Mathematical
School Programming
Arrays
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