Question

How to find the two elements in a vector whose sum is closest to zero in C++

Answer 1

#include <iostream>
#include <vector>
#include <algorithm> // sort
#include <climits> // INT_MAX
 
void findClosestToZero(const std::vector<int>& vec) {
    if (vec.size() < 2) {
        std::cout << "vec must have at least two elements." << std::endl;
        return;
    }
 
    // Step 1: Sort the vec
    std::vector<int> sortedvec = vec;
    std::sort(sortedvec.begin(), sortedvec.end());
 
    int left = 0, right = sortedvec.size() - 1;
    int closestSum = INT_MAX;
    int closestPair[2] = {0, 0};
 
    // Step 2: Use two-indexed technique
    while (left < right) {
        int sum = sortedvec[left] + sortedvec[right];
 
        // Update closest sum and pair if needed
        if (std::abs(sum) < std::abs(closestSum)) {
            closestSum = sum;
            closestPair[0] = sortedvec[left];
            closestPair[1] = sortedvec[right];
        }
 
        // Move indexeds
        if (sum < 0) {
            ++left; // Increase sum by moving left indexed
        } else {
            --right; // Decrease sum by moving right indexed
        }
    }
 
    // Output the result
    std::cout << "The two elements whose sum is closest to zero are: "
              << closestPair[0] << " and " << closestPair[1]
              << " with a sum of " << closestSum << "." << std::endl;
}
 
int main() {
    std::vector<int> vec = {23, -26, -88, -42, 55, 99, -11, 90, -13, 17, -31};
     
    findClosestToZero(vec);
}
 
 
/*
run:
 
The two elements whose sum is closest to zero are: -88 and 90 with a sum of 2.
 
*/

 

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