Created
March 28, 2019 14:08
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Merge sort (iterative)
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#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; | |
} |
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