C Exercises: Find two numbers that occur odd number of times in an array

Last update on March 18 2025 13:23:26 (UTC/GMT +8 hours)

70. Two Numbers Occurring Odd Number of Times

Write a program in C to find two numbers that occur an odd number of times in an array.

Expected Output:
The given array is: 6 7 3 6 8 7 6 8 3 3
The two numbers occuring odd number of times are: 3 & 6

The problem requires writing a C program to identify two numbers in an array that each occur an odd number of times. The program should efficiently traverse the array, keeping track of the frequency of each element, and then determine and display the two numbers that meet the specified condition.

Visual Presentation:

Sample Solution:

C Code:

#include <stdio.h>

// Function to find two numbers occurring odd number of times in an array
void TwoNumberOddOccure(int arr1[], int arr_size) {
int xor2 = arr1[0]; // Initialize xor2 with the first element of the array
int setbitno; // Variable to store the set bit number
int i;
int n = arr_size - 2; // Variable to store the size of the array - 2
int num1 = 0, num2 = 0; // Variables to store the two numbers occurring odd number of times

    // Calculate XOR of all elements in the array
for (i = 1; i < arr_size; i++)
        xor2 = xor2 ^ arr1[i];

    // Find the rightmost set bit in xor2
setbitno = xor2 & ~(xor2 - 1);

    // Traverse the array again and divide elements into two groups based on the rightmost set bit
for (i = 0; i < arr_size; i++) {
if (arr1[i] & setbitno)
            num1 = num1 ^ arr1[i]; // XOR operation to find first number
else
            num2 = num2 ^ arr1[i]; // XOR operation to find second number
    }

    // Print the two numbers occurring odd number of times
printf("The two numbers occuring odd number of times are: %d & %d ", num1, num2);
}

int main() {
int arr1[] = {6, 7, 3, 6, 8, 7, 6, 8, 3, 3};
int arr_size = sizeof(arr1) / sizeof(arr1[0]);
int i;  

    // Print the original array
printf("The given array is :  ");
for (i = 0; i < arr_size; i++) {
printf("%d  ", arr1[i]);
    } 
printf("\n");

    // Find and print two numbers occurring odd number of times
TwoNumberOddOccure(arr1, arr_size);
return 0;
}

Output:

The given array is :  6  7  3  6  8  7  6  8  3  3  
The two numbers occuring odd number of times are: 3 & 6 

Flowchart:/p>

For more Practice: Solve these Related Problems:

• Write a C program to find the two numbers that occur an odd number of times using bitwise XOR operations.
• Write a C program to identify two odd-occurring elements by counting frequencies with a hash table.
• Write a C program to determine the two numbers using sorting and then scanning for odd frequencies.
• Write a C program to recursively find the two elements that appear an odd number of times in an array.

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