用按位XOR作为偶数对进行计数

给定一个由N个整数组成的数组，任务是找到对(i，j)的对数，以使A [i] ^ A [j]为偶数。
例子：

Input: A[] =  { 5, 4, 7, 2, 1}
Output: 4
Since pair of A[] =
( 5, 4 ) = 1( 5, 7 ) = 2( 5, 2 ) = 7( 5, 1 ) = 4
( 4, 7 ) = 3( 4, 2 ) = 6( 4, 1 ) = 5
( 7, 2 ) = 5( 7, 1 ) = 6
( 2, 1 ) = 3
Total XOR even pair  = 4

Input: A[] = { 7, 2, 8, 1, 0, 5, 11 }
Output: 9
Since pair of A[] =
( 7, 2 ) = 5( 7, 8 ) = 15( 7, 1 ) = 6( 7, 0 ) = 7( 7, 5 ) = 2( 7, 11 ) = 12
( 2, 8 ) = 10( 2, 1 ) = 3( 2, 0 ) = 2( 2, 5 ) = 7( 2, 11 ) = 9
( 8, 1 ) = 9( 8, 0 ) = 8( 8, 5 ) = 13( 8, 11 ) = 3
( 1, 0 ) = 1( 1, 5 ) = 4( 1, 11 ) = 10
( 0, 5 ) = 5( 0, 11 ) = 11
( 5, 11 ) = 14

天真的方法是检查每个对，并打印偶数对。
下面是上述方法的实现：

C++

// C++ program to count pairs
// with XOR giving a even number
#include 
using namespace std;
 
// Function to count number of even pairs
int findevenPair(int A[], int N)
{
    int i, j;
 
    // variable for counting even pairs
    int evenPair = 0;
 
    // find all pairs
    for (i = 0; i < N; i++) {
        for (j = i + 1; j < N; j++) {
 
            // find XOR operation
            // check even or even
            if ((A[i] ^ A[j]) % 2 == 0)
                evenPair++;
        }
    }
 
    // return number of even pair
    return evenPair;
}
 
// Driver Code
int main()
{
 
    int A[] = { 5, 4, 7, 2, 1 };
    int N = sizeof(A) / sizeof(A[0]);
 
    // calling function findevenPair
    // and print number of even pair
    cout << findevenPair(A, N) << endl;
 
    return 0;
}

Java

// Java program to count pairs
// with XOR giving a even number
import java.io.*;
 
class GFG
{
 
// Function to count number of even pairs
static int findevenPair(int []A, int N)
{
    int i, j;
 
    // variable for counting even pairs
    int evenPair = 0;
 
    // find all pairs
    for (i = 0; i < N; i++)
    {
        for (j = i + 1; j < N; j++)
        {
 
            // find XOR operation
            // check even or even
            if ((A[i] ^ A[j]) % 2 == 0)
                evenPair++;
        }
    }
 
    // return number of even pair
    return evenPair;
}
 
// Driver Code
public static void main (String[] args)
{
    int A[] = { 5, 4, 7, 2, 1 };
    int N = A.length;
     
    // calling function findevenPair
    // and print number of even pair
    System.out.println(findevenPair(A, N));
}
}
 
// This code is contributed by inder_verma..

Python3

# Python3 program to count pairs
# with XOR giving a even number
 
  
# Function to count number of even pairs
def findevenPair(A, N):
 
    # variable for counting even pairs
    evenPair = 0
  
    # find all pairs
    for i in range(0, N):
        for j in range(i+1, N):
             
            # find XOR operation
            # check even or even
            if ((A[i] ^ A[j]) % 2 == 0):
                evenPair+=1
 
    # return number of even pair
    return evenPair;
  
# Driver Code
def main():
    A = [ 5, 4, 7, 2, 1 ]
    N = len(A)
  
    # calling function findevenPair
    # and prnumber of even pair
    print(findevenPair(A, N))
  
if __name__ == '__main__':
    main()
# This code is contributed by PrinciRaj1992

C#

// C# program to count pairs
// with XOR giving a even number
using System;
 
class GFG
{
 
// Function to count number of
// even pairs
static int findevenPair(int []A, int N)
{
    int i, j;
 
    // variable for counting even pairs
    int evenPair = 0;
 
    // find all pairs
    for (i = 0; i < N; i++)
    {
        for (j = i + 1; j < N; j++)
        {
 
            // find XOR operation
            // check even or even
            if ((A[i] ^ A[j]) % 2 == 0)
                evenPair++;
        }
    }
 
    // return number of even pair
    return evenPair;
}
 
// Driver Code
public static void Main ()
{
    int []A = { 5, 4, 7, 2, 1 };
    int N = A.Length;
     
    // calling function findevenPair
    // and print number of even pair
    Console.WriteLine(findevenPair(A, N));
}
}
 
// This code is contributed
// by inder_verma..

Javascript

// Javascript program to count pairs
// with XOR giving a even number
 
// Function to count number of even pairs
function findevenPair(A, N)
{
    let i, j;
 
    // variable for counting even pairs
    let evenPair = 0;
 
    // find all pairs
    for (i = 0; i < N; i++) {
        for (j = i + 1; j < N; j++) {
 
            // find XOR operation
            // check even or even
            if ((A[i] ^ A[j]) % 2 == 0)
                evenPair++;
        }
    }
 
    // return number of even pair
    return evenPair;
}
 
// Driver Code
let A = [ 5, 4, 7, 2, 1 ];
let N = A.length;
 
// calling function findevenPair
// and print number of even pair
document.write(findevenPair(A, N));
 
// This code is contributed by souravmahato348.

输出：

4

时间复杂度： O(n ^ 2)
一种有效的解决方案是计数与位异或对作为奇数即oddEvenpairs。然后返回totalPairs –奇数偶数对，其中totalPairs =(N *(N-1)/ 2)和oddEvenPairs =数*(N –计数) 。作为，将提供偶按位异或的对是：

Even, Even 
Odd, Odd

因此，找到同时具有奇数和偶数元素的对数并从总数中减去。对。
下面是上述方法的实现：

C++

// C++ program to count pairs
// with XOR giving a even number
#include 
using namespace std;
 
// Function to count number of even pairs
int findEvenPair(int A[], int N)
{
    int count = 0;
 
    // find all pairs
    for (int i = 0; i < N; i++) {
        if (A[i] % 2 != 0)
            count++;
    }
 
    int totalPairs = (N * (N - 1) / 2);
    int oddEvenPairs = count * (N - count);
 
    // return number of even pair
    return totalPairs - oddEvenPairs;
}
 
// Driver Code
int main()
{
    int a[] = { 5, 4, 7, 2, 1 };
    int n = sizeof(a) / sizeof(a[0]);
 
    // calling function findEvenPair
    // and print number of even pair
    cout << findEvenPair(a, n) << endl;
 
    return 0;
}

Java

// Java  program to count pairs
// with XOR giving a even number
 
import java.io.*;
 
class GFG {
    // Function to count number of even pairs
static int findEvenPair(int A[], int N)
{
    int count = 0;
 
    // find all pairs
    for (int i = 0; i < N; i++) {
        if (A[i] % 2 != 0)
            count++;
    }
 
    int totalPairs = (N * (N - 1) / 2);
    int oddEvenPairs = count * (N - count);
 
    // return number of even pair
    return totalPairs - oddEvenPairs;
}
 
// Driver Code
     
    public static void main (String[] args) {
     
    int a[] = { 5, 4, 7, 2, 1 };
    int n = a.length;
    // calling function findEvenPair
    // and print number of even pair
    System.out.println(findEvenPair(a, n));
    }
//This code is contributed by akt_mit   
}

Python3

# python program to count pairs
# with XOR giving a even number
 
# Function to count number of even pairs
def findEvenPair(A, N):
    count = 0
  
    # find all pairs
    for i in range(0,N):
        if (A[i] % 2 != 0):
            count+=1
  
    totalPairs = (N * (N - 1) / 2)
    oddEvenPairs = count * (N - count)
  
    # return number of even pair
    return (int)(totalPairs - oddEvenPairs)
 
# Driver Code
def main():
    a = [ 5, 4, 7, 2, 1 ]
    n = len(a)
  
    # calling function findEvenPair
    # and pr number of even pair
    print(findEvenPair(a, n))
  
if __name__ == '__main__':
    main()
     
# This code is contributed by 29AjayKumar

C＃

// C# program to count pairs
// with XOR giving a even number
  
using System;
  
public class GFG {
    // Function to count number of even pairs
    static int findEvenPair(int []A, int N)
    {
        int count = 0;
 
        // find all pairs
        for (int i = 0; i < N; i++) {
            if (A[i] % 2 != 0)
                count++;
        }
 
        int totalPairs = (N * (N - 1) / 2);
        int oddEvenPairs = count * (N - count);
 
        // return number of even pair
        return totalPairs - oddEvenPairs;
    }
 
    // Driver Code
      
    public static void Main() {
      
    int []a = { 5, 4, 7, 2, 1 };
    int n = a.Length;
    // calling function findEvenPair
    // and print number of even pair
    Console.Write(findEvenPair(a, n));
    }
}
 
// This code is contributed by 29AjayKumar

输出：

4

时间复杂度： O(n)