Question

How to find the two elements in an array whose sum is closest to zero in C

Answer 1

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <math.h>
 
int compareInts(const void *a, const void *b) {
    return (*(int *)a - *(int *)b);
}
 
// Finds the two elements whose sum is closest to zero
void findClosestToZero(int arr[], int size) {
    if (size < 2) {
        printf("Array must have at least two elements.\n");
        return;
    }
 
    // Step 1: Sort the array
    qsort(arr, size, sizeof(int), compareInts);
 
    int left = 0;
    int right = size - 1;
    int closestSum = INT_MAX;
    int closestPair[2] = {0, 0};
 
    // Step 2: Use two-indexes technique
    while (left < right) {
        int sum = arr[left] + arr[right];
 
        // Update closest sum and pair if needed
        if (abs(sum) < abs(closestSum)) {
            closestSum = sum;
            closestPair[0] = arr[left];
            closestPair[1] = arr[right];
        }
 
        // Move indexess
        if (sum < 0) {
            left++;  // Increase sum
        } else {
            right--; // Decrease sum
        }
    }
 
    // Output the result
    printf("The two elements whose sum is closest to zero are: %d and %d with a sum of %d.\n",
           closestPair[0], closestPair[1], closestSum);
}
 
int main() {
    int arr[] = {23, -26, -88, -42, 55, 99, -11, 90, -13, 17, -31};
    int size = sizeof(arr) / sizeof(arr[0]);
 
    findClosestToZero(arr, size);
 
    return 0;
}
 
 
 
/*
run:
 
The two elements whose sum is closest to zero are: -88 and 90 with a sum of 2.
 
*/

 

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