Merge sort (iterative)

mergesort_i.cpp

#include <iostream>
#include <vector>

void merge(std::vector<int>& nums, int start, int chunk_size) {
    //iterate through first partition (start -> start+chunk_size) while
    //iterating through second partition and choose the smallest number
    std::vector<int> result; 
    int mid = start + (chunk_size);
    int merge_size = chunk_size*2;
    for (int i=start,j=mid; result.size()<merge_size; ) {
        if (j>=start+merge_size || (i-start<chunk_size && nums[i]<nums[j])) 
            result.push_back(nums[i++]);
        else
            result.push_back(nums[j++]);
    }

    //copy sorted partitions (result) back to main array (nums)
    for (int n=0; n<result.size(); n++) {
        nums[start+n] = result[n];
    }
}

//iterative merge sort
void merge_sort(std::vector<int>& nums) {
    int chunk_size = 1; //start merging one element at a time
    for ( ; chunk_size <= nums.size()-1; chunk_size*=2) {
        //iterate through this pass merging adjacent chunks
        for (int idx=0; idx<nums.size(); idx+=(chunk_size*2)) {
            int merge_size = chunk_size*2;
            if (nums.size()-idx < merge_size)
                merge_size = nums.size()-idx;
            if (merge_size==1)
                continue;
            merge(nums, idx, chunk_size);
        }
    }
}

template <class T>
void print_v(const std::vector<T>& nums) {
    for (int i=0; i<nums.size(); i++) {
        std::cout << nums[i] << " ";
    }
    std::cout << std::endl;
}

int main()
{
    std::vector<int> nums { 4,9,6,3,8,5,1,7 };
    print_v(nums);
    merge_sort(nums);
    print_v(nums);

    return 0;
}