[병합 정렬] 백준 1517 버블 소트 C++

 

https://www.acmicpc.net/problem/1517

#include<iostream>

using namespace std;

int num[500000];
int tempArr[500000];
long long ans; /// 최대 100000C2

void mergeSort(int s, int e) {
    if (s >= e) return;
    int m = (s + e) / 2;

    mergeSort(s, m);
    mergeSort(m + 1, e);

    int l = s, cur = s, r = m + 1;
    while ((l <= m) && (r <= e)) {
        if (num[l] <= num[r]) tempArr[cur++] = num[l++];
        else {
            tempArr[cur++] = num[r++];
            ans += (m - l + 1); // 왼쪽 배열의 크기만큼
        }
    }

    while (l <= m) tempArr[cur++] = num[l++];
    while (r <= e) tempArr[cur++] = num[r++];
    for (int i = s; i <= e; i++) num[i] = tempArr[i];
}

int main(int argc, char** argv)
{
    ios_base::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);

    int n;
    cin >> n;

    for (int i = 0; i < n; i++) {
        cin >> num[i];
    }

    ans = 0;
    mergeSort(0, n - 1);

    cout << ans;

    return 0;
}