1#include <iostream>2using namespace std;3int n, s, a[100005], t[100005], i;4void mergesort(int l, int r)5{6    if (l == r)7        return;8    int mid = (l + r) / 2;9    int p = l;10    int i = l;11    int j = mid + 1;12    mergesort(l, mid);13    mergesort(mid + 1, r);14    while (i <= mid && j <= r)15    {16        if (a[j] < a[i])17        {18            s += mid - i + 1;19            t[p] = a[j];20            p++;21            j++;22        }23        else24        {25            t[p] = a[i];26            p++;27            i++;28        }29    }30    while (i <= mid)31    {32        t[p] = a[i];33        p++;34        i++;35    }36    while (j <= r)37    {38        t[p] = a[j];39        p++;40        j++;41    }42    for (i = l; i <= r; i++)43        a[i] = t[i];44}45int main()46{47    cin >> n;48    for (i = 1; i <= n; i++)49        cin >> a[i];50    mergesort(1, n);51    cout << s << endl;52    return 0;53}

输入：6 2 6 3 4 5 1 输出：_________