Find sum of xor of all unordered triplets of the array

Last Updated : 27 Aug, 2022

Given an array A, consisting of N non-negative integers, find the sum of xor of all unordered triplets of the array. For unordered triplets, the triplet (A[i], A[j], A[k]) is considered the same as triplets (A[j], A[i], A[k]) and all the other permutations.
Since the answer can be large, calculate its mod to 10037.

Examples:

Input : A = [3, 5, 2, 18, 7]
Output : 132

Input : A = [140, 1, 66]
Output : 207

Naive Approach
Iterate over all the unordered triplets and add xor of each to the sum.

Efficient Approach

An important point to observe is that xor is independent of all the bits. So we can do the required computation over each bit individually.
Let's consider the k'th bit of all the array elements. If the number of unordered triplets is k'th bit xor 1 be C, we can simply add C * 2^k to the answer. Let the number of elements whose k'th bit is 1 be X and whose k'th bit is 0 be Y. Then find the unordered triplets whose k'th bits xor to 1 can be formed using two cases:
1. Only one of the three elements has k'th bit 1.
2. All three of them have k'th bit 1.
Number of ways to select 3 elements having k'th bit 1 = {X \choose 3}
Number of ways to select 1 element with k'th bit 1 and rest with 0 = X * {Y \choose 3}
We will use nCr mod p to compute the combinatorial function values.

Below is the implementation of the above approach.

C++

// C++ program to find sum of xor of 
// all unordered triplets of the array 
#include <bits/stdc++.h> 

using namespace std; 

// Iterative Function to calculate 
// (x^y)%p in O(log y) 
int power(int x, int y, int p) 
{ 
    // Initialize result 
    int res = 1; 

    // Update x if it is more than or 
    // equal to p 
    x = x % p; 
    

    while (y > 0) 
    { 
        // If y is odd, multiply x 
        // with result 
        if (y & 1) 
            res = (res * x) % p; 

        // y must be even now 
        y = y >> 1; // y = y/2 
        x = (x * x) % p; 
    } 
    return res; 
} 

// Returns n^(-1) mod p 
int modInverse(int n, int p) 
{ 
    return power(n, p - 2, p); 
} 

// Returns nCr % p using Fermat's little 
// theorem. 
int nCrModPFermat(int n, int r, int p) 
{ 
    // Base case 
    if (r == 0) 
        return 1; 
    if (n < r) 
        return 0; 
    
    // Fill factorial array so that we 
    // can find all factorial of r, n 
    // and n-r 
    int fac[n + 1]; 
    fac[0] = 1; 
    for (int i = 1; i <= n; i++) 
        fac[i] = fac[i - 1] * i % p; 

    return (fac[n] * modInverse(fac[r], p) % p 
            * modInverse(fac[n - r], p) % p) % p; 
} 

// Function returns sum of xor of all 
// unordered triplets of the array 
int SumOfXor(int a[], int n) 
{ 

    int mod = 10037; 

    int answer = 0; 

    // Iterating over the bits 
    for (int k = 0; k < 32; k++) 
    { 
        // Number of elements whith k'th bit 
        // 1 and 0 respectively 
        int x = 0, y = 0; 

        for (int i = 0; i < n; i++) 
        { 
            // Checking if k'th bit is 1 
            if (a[i] & (1 << k)) 
                x++; 
            else
                y++; 
        } 
        // Adding this bit's part to the answer 
        answer += ((1 << k) % mod * 
                (nCrModPFermat(x, 3, mod) 
                    + x * nCrModPFermat(y, 2, mod)) 
                % mod) % mod; 
    } 
    return answer; 
} 
// Drivers code 
int main() 
{ 
    int n = 5; 
    int A[n] = { 3, 5, 2, 18, 7 }; 

    cout << SumOfXor(A, n); 

    return 0; 
}

Java

// Java program to find sum of xor of
// all unordered triplets of the array
class GFG{

// Iterative Function to calculate
// (x^y)%p in O(log y)
static int power(int x, int y, int p)
{
    
    // Initialize result
    int res = 1;

    // Update x if it is more than or
    // equal to p
    x = x % p;

    while (y > 0)
    {
        
        // If y is odd, multiply x
        // with result
        if ((y & 1) == 1)
            res = (res * x) % p;

        // y must be even now
        y = y >> 1; // y = y/2
        x = (x * x) % p;
    }
    return res;
}

// Returns n^(-1) mod p
static int modInverse(int n, int p)
{
    return power(n, p - 2, p);
}

// Returns nCr % p using Fermat's little
// theorem.
static int nCrModPFermat(int n, int r, int p)
{
    
    // Base case
    if (r == 0)
        return 1;
    if (n < r)
        return 0;

    // Fill factorial array so that we
    // can find all factorial of r, n
    // and n-r
    int fac[] = new int[n + 1];
    fac[0] = 1;
    for(int i = 1; i <= n; i++)
        fac[i] = fac[i - 1] * i % p;

    return (fac[n] * modInverse(fac[r], p) % p * 
                     modInverse(fac[n - r], p) %
                                            p) % p;
}

// Function returns sum of xor of all
// unordered triplets of the array
static int SumOfXor(int a[], int n)
{

    int mod = 10037;
    int answer = 0;

    // Iterating over the bits
    for(int k = 0; k < 32; k++)
    {
        
        // Number of elements whith k'th bit
        // 1 and 0 respectively
        int x = 0, y = 0;

        for(int i = 0; i < n; i++)
        {
            
            // Checking if k'th bit is 1
            if ((a[i] & (1 << k)) != 0)
                x++;
            else
                y++;
        }
        // Adding this bit's part to the answer
        answer += ((1 << k) % mod * 
                   (nCrModPFermat(x, 3, mod) + x * 
                    nCrModPFermat(y, 2, mod)) % 
                                        mod) % mod;
    }
    return answer;
}

// Driver code
public static void main(String[] args)
{
    int n = 5;
    int A[] = { 3, 5, 2, 18, 7 };

    System.out.println(SumOfXor(A, n));
}
}

// This code is contributed by jrishabh99

Python3

# Python3 program to find sum of xor of 
# all unordered triplets of the array 

# Iterative Function to calculate 
# (x^y)%p in O(log y) 
def power(x, y, p): 
    
    # Initialize result 
    res = 1

    # Update x if it is more than or 
    # equal to p 
    x = x % p 

    while (y > 0): 
        # If y is odd, multiply x 
        # with result 
        if (y & 1): 
            res = (res * x) % p 

        # y must be even now 
        y = y >> 1#y = y/2 
        x = (x * x) % p 
    return res 

# Returns n^(-1) mod p 
def modInverse(n, p): 
    return power(n, p - 2, p) 

# Returns nCr % p using Fermat's little 
# theorem. 
def nCrModPFermat(n, r, p): 
    
    # Base case 
    if (r == 0): 
        return 1
    if (n < r): 
        return 0

    # Fill factorial array so that we 
    # can find all factorial of r, n 
    # and n-r 
    fac = [0]*(n + 1) 
    fac[0] = 1
    for i in range(1, n + 1): 
        fac[i] = fac[i - 1] * i % p 

    return (fac[n] * modInverse(fac[r], p) % p *
            modInverse(fac[n - r], p) % p) % p 

# Function returns sum of xor of all 
# unordered triplets of the array 
def SumOfXor(a, n): 

    mod = 10037

    answer = 0

    # Iterating over the bits 
    for k in range(32): 
        
        # Number of elements whith k'th bit 
        # 1 and 0 respectively 
        x = 0
        y = 0

        for i in range(n): 
            
            # Checking if k'th bit is 1 
            if (a[i] & (1 << k)): 
                x += 1
            else: 
                y += 1
        # Adding this bit's part to the answer 
        answer += ((1 << k) % mod * (nCrModPFermat(x, 3, mod) 
                    + x * nCrModPFermat(y, 2, mod)) 
                % mod) % mod 

    return answer 

# Drivers code 
if __name__ == '__main__': 
    n = 5
    A=[3, 5, 2, 18, 7] 

    print(SumOfXor(A, n)) 

# This code is contributed by mohit kumar 29

// C# program to find sum of xor of
// all unordered triplets of the array
using System;
class GFG{

// Iterative Function to calculate
// (x^y)%p in O(log y)
static int power(int x, int y, int p)
{
    
    // Initialize result
    int res = 1;

    // Update x if it is more than or
    // equal to p
    x = x % p;

    while (y > 0)
    {
        
        // If y is odd, multiply x
        // with result
        if ((y & 1) == 1)
            res = (res * x) % p;

        // y must be even now
        y = y >> 1; // y = y/2
        x = (x * x) % p;
    }
    return res;
}

// Returns n^(-1) mod p
static int modInverse(int n, int p)
{
    return power(n, p - 2, p);
}

// Returns nCr % p using Fermat's little
// theorem.
static int nCrModPFermat(int n, int r, int p)
{
    
    // Base case
    if (r == 0)
        return 1;
    if (n < r)
        return 0;

    // Fill factorial array so that we
    // can find all factorial of r, n
    // and n-r
    int []fac = new int[n + 1];
    fac[0] = 1;
    for(int i = 1; i <= n; i++)
        fac[i] = fac[i - 1] * i % p;

    return (fac[n] * modInverse(fac[r], p) % p * 
                     modInverse(fac[n - r], p) %
                                            p) % p;
}

// Function returns sum of xor of all
// unordered triplets of the array
static int SumOfXor(int []a, int n)
{
    int mod = 10037;
    int answer = 0;

    // Iterating over the bits
    for(int k = 0; k < 32; k++)
    {
        
        // Number of elements whith k'th bit
        // 1 and 0 respectively
        int x = 0, y = 0;

        for(int i = 0; i < n; i++)
        {
            
            // Checking if k'th bit is 1
            if ((a[i] & (1 << k)) != 0)
                x++;
            else
                y++;
        }
        // Adding this bit's part to the answer
        answer += ((1 << k) % mod * 
                   (nCrModPFermat(x, 3, mod) + x * 
                    nCrModPFermat(y, 2, mod)) % 
                                        mod) % mod;
    }
    return answer;
}

// Driver code
public static void Main(String[] args)
{
    int n = 5;
    int []A = { 3, 5, 2, 18, 7 };

    Console.WriteLine(SumOfXor(A, n));
}
}

// This code is contributed by gauravrajput1

JavaScript

<script>

// Javascript program to find sum of xor of
// all unordered triplets of the array

// Iterative Function to calculate
// (x^y)%p in O(log y)
function power(x, y, p)
{
     
    // Initialize result
    let res = 1;
 
    // Update x if it is more than or
    // equal to p
    x = x % p;
 
    while (y > 0)
    {
         
        // If y is odd, multiply x
        // with result
        if ((y & 1) == 1)
            res = (res * x) % p;
 
        // y must be even now
        y = y >> 1; // y = y/2
        x = (x * x) % p;
    }
    return res;
}
 
// Returns n^(-1) mod p
function modInverse(n, p)
{
    return power(n, p - 2, p);
}
 
// Returns nCr % p using Fermat's little
// theorem.
function nCrModPFermat(n, r, p)
{
     
    // Base case
    if (r == 0)
        return 1;
    if (n < r)
        return 0;
 
    // Fill factorial array so that we
    // can find all factorial of r, n
    // and n-r
    let fac = Array.from({length: n+1}, (_, i) => 0);
    fac[0] = 1;
    for(let i = 1; i <= n; i++)
        fac[i] = fac[i - 1] * i % p;
 
    return (fac[n] * modInverse(fac[r], p) % p *
                     modInverse(fac[n - r], p) %
                                            p) % p;
}
 
// Function returns sum of xor of all
// unordered triplets of the array
function SumOfXor(a, n)
{
 
    let mod = 10037;
    let answer = 0;
 
    // Iterating over the bits
    for(let k = 0; k < 32; k++)
    {
         
        // Number of elements whith k'th bit
        // 1 and 0 respectively
        let x = 0, y = 0;
 
        for(let i = 0; i < n; i++)
        {
             
            // Checking if k'th bit is 1
            if ((a[i] & (1 << k)) != 0)
                x++;
            else
                y++;
        }
        // Adding this bit's part to the answer
        answer += ((1 << k) % mod *
                   (nCrModPFermat(x, 3, mod) + x *
                    nCrModPFermat(y, 2, mod)) %
                                        mod) % mod;
    }
    return answer;
}

// Driver Code
    
    let n = 5;
    let A = [ 3, 5, 2, 18, 7 ];
 
    document.write(SumOfXor(A, n));
               
</script>

Output:

Time Complexity : O(32 * N)

Auxiliary Space: O(N) since we are storing N elements in array data structure.

Find sum of XNOR of all unordered pairs from given Array

king_tsar

Improve

Article Tags :

Practice Tags :

Find sum of xor of all unordered triplets of the array

Similar Reads

Thank You!

What kind of Experience do you want to share?