// Prog: merge_sort.cpp
// implements and tests merge-sort on random input
#include
#include
#include
typedef std::vector::iterator Vit;
// PRE: [begin, middle), [middle, end) are valid ranges; in
// both of them, the elements are in ascending order
void merge (Vit begin, Vit middle, Vit end)
{
const int n = end - begin; // total number of cards
std::vector deck(n); // new deck to be built
Vit left = begin; // top card of left deck
Vit right = middle; // top card of right deck
for (Vit d = deck.begin(); d != deck.end(); ++d)
// put next card onto new deck
if (left == middle) *d = *right++; // left deck is empty
else if (right == end) *d = *left++; // right deck is empty
else if (*left < *right) *d = *left++; // smaller top card left
else *d = *right++; // smaller top card right
// copy new deck back into [begin, end)
Vit d = deck.begin();
while (begin != middle) *begin++ = *d++;
while (middle != end) *middle++ = *d++;
}
// PRE: [begin, end) is a valid range
// POST: the elements *p, p in [begin, end) are in ascending order
void merge_sort (Vit begin, Vit end)
{
const int n = end - begin;
if (n <= 1) return; // nothing to do
const Vit middle = begin + n/2;
merge_sort (begin, middle); // sort first half
merge_sort (middle, end); // sort second half
merge (begin, middle, end); // merge both halfs
}
int main()
{
// input of number of values to be sorted
int n;
std::cin >> n;
std::vector v(n);
std::cout << "Sorting " << n << " integers...\n";
// create sequence:
for (int i=0; i
