C Exercises: Total of two indices values equal a target

Last update on March 21 2025 12:37:22 (UTC/GMT +8 hours)

1. Two-Sum Indices Variants

Write a C program to get the indices of two numbers in a given array of integers. This will enable you to get the sum of two numbers equal to a specific target.

C Code:

#include <stdio.h>
#include <stdlib.h>

struct object {
    int val;
    int index;
};

static int compare(const void *a, const void *b)
{
    return ((struct object *) a)->val - ((struct object *) b)->val;
}

static int * two_sum(int *nums, int nums_size, int target)
{
    int i, j;
    struct object *objes = malloc(nums_size * sizeof(*objes));
    for (i = 0; i < nums_size; i++) {
        objes[i].val = nums[i];
        objes[i].index = i;
    }
    qsort(objes, nums_size, sizeof(*objes), compare);
    
    int *results = malloc(2 * sizeof(int));
    i = 0;
    j = nums_size - 1;
    while (i < j) {
        int diff = target - objes[i].val;
        if (diff > objes[j].val) {
            while (++i < j && objes[i].val == objes[i - 1].val) {}
        } else if (diff < objes[j].val) {
            while (--j > i && objes[j].val == objes[j + 1].val) {}
        } else {
            results[0] = objes[i].index;
            results[1] = objes[j].index;
            return results;
        }
    }
    return NULL;
}

int main(void)
{
    int nums[] = { 4, 2, 1, 5 };
    int ctr = sizeof(nums) / sizeof(*nums);
    int target = 7;
	int i;
	printf("Original Array: ");
	for(i=0; i<ctr; i++)
    {
        printf("%d  ", nums[i]);
    }
    printf("\nTarget Value: %d", target);
    int *indexes = two_sum(nums, ctr, target);
    if (indexes != NULL) {
		printf("\nIndices of the two numbers whose sum equal to target value: %d", target);
        printf("\n%d %d\n", indexes[0], indexes[1]);
    } 
	else
	{
        printf("Not found or matched\n");
    }

    return 0;
}

Sample Output:

Original Array: 4  2  1  5  
Target Value: 7
Indices of the two numbers whose sum equal to target value: 7
1 3

Pictorial Presentation:

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C program to find indices of two numbers in an unsorted array that sum to a given target using a hash table.
• Write a C program to locate indices of two numbers in a sorted array whose sum equals the target using binary search for complements.
• Write a C program to identify indices of two numbers in a circular array that sum to a specified target.
• Write a C program to find indices of two numbers that sum to a target, ensuring the solution returns the smallest possible index pair.

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