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MergeSort.cpp
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MergeSort.cpp
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#include <algorithm>
#include <iostream>
#include "RandomData.h"
using namespace std;
const int SIZE = 100;
void Merge(vector<int>::iterator itr, const vector<int> &part1, const vector<int> &part2)
{
vector<int>::const_iterator itr1 = part1.begin();
vector<int>::const_iterator itr2 = part2.begin();
while (itr1 != part1.end() && itr2 != part2.end())
{
if (*itr1 < *itr2)
{
*itr++ = *itr1++;
}
else
{
*itr++ = *itr2++;
}
}
while (itr1 != part1.end())
{
*itr++ = *itr1++;
}
while (itr2 != part2.end())
{
*itr++ = *itr2++;
}
}
void MergeSort(vector<int> &v)
{
if (v.size() <= 1)
{
return;
}
vector<int>::iterator middle = v.begin() + (v.end() - v.begin()) / 2;
vector<int> part1(v.begin(), middle);
vector<int> part2(middle, v.end());
MergeSort(part1);
MergeSort(part2);
Merge(v.begin(), part1, part2);
return;
}
// Because we pass v.begin() and v.end() to this function, we can't
// declara the parameter of these two iterators as references.
void MergeSort(vector<int>::iterator first, vector<int>::iterator last)
{
// !!WATCH OUT!! We need to check last is at least one after first.
// Otherwise, first equals to last, then MergeSort would get into
// infinte recursion when MergeSort(first, first).
if (first + 1 >= last)
{
return;
}
vector<int>::iterator middle = first + (last - first) / 2;
MergeSort(first, middle);
MergeSort(middle, last);
inplace_merge(first, middle, last);
return;
}
#ifndef EXPORTED
int main()
{
vector<int> v;
initializeVector(v, SIZE);
printVector(v);
// MergeSort(v);
MergeSort(v.begin(), v.end());
printVector(v);
return 0;
}
#endif