重点 ：归并排序求逆序对

归并排序模板

#include <iostream>
#include <cstdio>

using namespace std;
const int N = 100010;

int n;
int q[N], tmp[N];

void merge_sort(int q[], int l, int r)
{
    if (l >= r) return;

    int mid = l + r >> 1;
    merge_sort(q, l, mid);
    merge_sort(q, mid + 1, r);

    int k = 0, i = l, j = mid + 1;
    while (i <= mid && j <= r)
        if (q[i] <= q[j]) tmp[k++] = q[i++];
        else tmp[k++] = q[j++];

    while (i <= mid) tmp[k++] = q[i++];
    while (j <= r) tmp[k++] = q[j++];

    for (int i = l, j = 0; i <= r; i++, j++)
        q[i] = tmp[j];
}

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

    merge_sort(q, 0, n - 1);

    for (int i = 0; i < n; i++)
        cout << q[i] << ' ';

    return 0;
}

归并排序求逆序对

#include <iostream>
#include <cstdio>

using namespace std;
const int N = 100010;

int n;
int q[N], tmp[N];

void merge_sort(int q[], int l, int r)
{
    if (l >= r) return;

    int mid = l + r >> 1;
    merge_sort(q, l, mid);
    merge_sort(q, mid + 1, r);

    int k = 0, i = l, j = mid + 1;
    while (i <= mid && j <= r)
        if (q[i] <= q[j]) tmp[k++] = q[i++];
        else tmp[k++] = q[j++];

    while (i <= mid) tmp[k++] = q[i++];
    while (j <= r) tmp[k++] = q[j++];

    for (int i = l, j = 0; i <= r; i++, j++)
        q[i] = tmp[j];
}

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

    merge_sort(q, 0, n - 1);

    for (int i = 0; i < n; i++)
        cout << q[i] << ' ';

    return 0;
}