[STL] qsort 구현

#include <iostream>
#include <cstdio>
#include <vector>
 
using namespace std;
 
template <typename T>
void _swap(T &a, T &b)
{
    T t = a;
    a = b;
    b = t;
}
 
template <typename T, typename C>
void _qsort(T start, T end, C comp)
{
    if (start == end)
        return;
 
    _swap(*start, *((end - start) / 2 + start));
 
    T pivot = start;
    T left = start + 1;
    T right = end - 1;
 
    while (left <= right)
    {
        while (left <= right && !comp(*pivot, *left))
            left++;
        while (left <= right && !comp(*right, *pivot))
            right--;
 
        if (left <= right)
            _swap(*left, *right);
    }
 
    _swap(*pivot, *right);
    _qsort(start, right, comp);
    _qsort(right + 1, end, comp);
}
 
template <typename T1, typename T2>
struct _pair {
    T1 first;
    T2 second;
 
    bool operator <(const _pair<T1, T2> &a) {
        if (first == a.first)
            return second < a.second;
        return first < a.first;
    }
};
 
bool comp(const _pair<int, int> &a, const _pair<int, int> &b)
{
    if (a.second == b.second)
        return a.first < b.first;
    return a.second < b.second;
}
 
_pair<int, int> arr[6];
vector<_pair<int, int> > vc;
int main()
{
    int n;
    scanf("%d", &n);
 
    for (int i = 0; i < n; i++)
    {
        int x, y;
        scanf("%d %d", &x, &y);
 
        arr[i] = { x,y };
        vc.push_back({ x,y });
    }
    _qsort(arr, arr + n, comp);
    _qsort(vc.begin(), vc.end(), comp);
 
    for (auto i : arr)
        printf("%d %d\n", i.first, i.second);
    printf("\n\n");
    for (auto i : vc)
        printf("%d %d\n", i.first, i.second);
 
    return 0;
}
 

출처 :: https://github.com/baactree/Algorithm/blob/master/Stl/sort.cpp