C Exercises: Print all possible combinations of r elements in a given array

Last update on March 18 2025 13:23:20 (UTC/GMT +8 hours)

82. Combinations of r Elements from Array

Write a program in C to print all possible combinations of r elements in a given array.

Expected Output:
The given array is:
1 5 4 6 8 The combination from by the number of elements are: 3
The combinations are:
1 5 4 6
1 5 4 8
1 5 6 8
1 4 6 8
5 4 6 8

The task is to write a C program that prints all possible combinations of r elements from a given array. The program should generate and display each unique combination of the specified number of elements. The output should list all the possible combinations formed from the array elements for the given value of r.

Sample Solution:

C Code:

#include <stdio.h>

// Function to generate combinations
void makeCombination(int arr1[], int data[], int st, int end, int index, int r);

// Function to display combinations
void CombinationDisplay(int arr1[], int n, int r) {
    int data[r]; // Temporary array to store the combination
    makeCombination(arr1, data, 0, n - 1, 0, r); // Generate combinations
}

// Recursive function to generate combinations
void makeCombination(int arr1[], int data[], int st, int end, int index, int r) {
    // Base case: if index equals r, print the combination
    if (index == r) {
        for (int j = 0; j < r; j++)
            printf("%d ", data[j]); // Print the combination elements
        printf("\n"); // Move to the next line for the next combination
        return;
    }

    // Generate combinations recursively
    for (int i = st; i <= end && end - i + 1 >= r - index; i++) {
        data[index] = arr1[i]; // Fill data[] with elements of arr1[] for the current combination
        makeCombination(arr1, data, i + 1, end, index + 1, r); // Recursively generate combinations
    }
}

int main() {
    int arr1[] = {1, 5, 4, 6, 8};
    int r = 4; // Number of elements in each combination
    int n = sizeof(arr1) / sizeof(arr1[0]); // Calculate array size
    int i;

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

    printf("The combination from by the number of elements are: %d\n", r);
    printf("The combinations are: \n");
    CombinationDisplay(arr1, n, r); // Display combinations
    return 0;
}

Output:

The given array is:  
1  5  4  6  8  
The combination from by the number of elements are: 4
The combinations are: 
1 5 4 6 
1 5 4 8 
1 5 6 8 
1 4 6 8 
5 4 6 8 

Visual Presentation:

Flowchart 1:

Flowchart 2:

For more Practice: Solve these Related Problems:

• Write a C program to generate all possible combinations of r elements from a given array using recursion.
• Write a C program to print all combinations of r elements in lexicographical order.
• Write a C program to generate combinations and then count the total number of combinations.
• Write a C program to generate and store all r-element combinations in a dynamically allocated 2D array.

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