Question

How to iterate a vector from the middle outward (stepping left and right alternately) in C++

Answer 1

#include <iostream>
#include <vector>

// Start at mid = n/2, then move mid-1, mid+1, mid-2, mid+2, … until the vector is fully covered.

int main() {
    std::vector<int> vec = {0,1,2,3,4,5,6,7};

    int n = vec.size();
    int mid = n / 2;               // middle index for even-sized vector
    int left = mid - 1;            // start expanding left
    int right = mid;               // start expanding right

    // Iterate outward from the middle
    while (left >= 0 || right < n) {

        if (right < n) {
            std::cout << vec[right] << " ";
            right++;
        }

        if (left >= 0) {
            std::cout << vec[left] << " ";
            left--;
        }
    }
}



/*
run:

4 3 5 2 6 1 7 0 

*/

 

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