Ultra quicksort

# Meaning of problems
n integers different sequences processed by the ranking algorithm exchanging adjacent two sequence elements, in ascending order until the sequence is determined to be exchanged over many times quicksort

# Problem solution
method for sorting by exchanging only the adjacent values actually bubble sort, each set of adjacent values to find a reverse be exchanged during sorting, so that the entire sequence will reverse to the number of -1, the final after sorted, the number of reverse apparently 0, so the number of times for a minimum of switching is required bubble sort in reverse order of the sequence a

 1 #include<bits/stdc++.h>
 2 #define ll long long
 3 using namespace std;
 4 const int N=1e6+10;
 5 int n;
 6 int a[N];
 7 int ans[N];
 8 ll merge_sort(int l,int r){
 9    if(l>=r) return 0;
10    int mid=l+r>>1;
11    ll res=merge_sort(l,mid)+merge_sort(mid+1,r);
12 
13    int k = 0,i = l,j = mid+1;
14    while(i <= mid && j <= r){
15       if(a[i] <= a[j])
16          ans[k++]=a[i++];
17       else{
18          ans[k++]=a[j++];
19          res+=mid-i+1;
20       }
21    }
22    while(i <= mid) ans[k++] = a[i++];
23    while(j <= r) ans[k++] = a[j++];
24 
25    for(int i = l,j = 0; i <= r; i++,j++)
26       a[i]=ans[j];
27    return res;
28 }
29 int main(){
30    ios::sync_with_stdio(0);
31    cin.tie(0);
32    cout.tie(0);
33    while(cin>>n&&n){
34       for(int i=0;i<n;i++)
35          cin>>a[i];
36 
37       cout<<merge_sort(0,n-1)<<endl;
38    }
39 }