CDOJ1583- Fenwick tree (2017 UESTC Training for Data Structures)

Portal: CDOJ1583

Subject to the effect:

You arranged two number n, you ask from a first neighboring exchange by a second number of permutations becomes minimum number of steps arranged

Topic ideas:

Because only Swap adjacent number, so we can think of greedy direct order from left to right will become the first second,

Exchange a number of times each number is moved to the position from the finish, where we can be a good deal to think of Fenwick tree

We first find the number of reverse arrangement only the first number in the array ranked second, and then find an array of ranking is the answer

AC Code:

#include<bits/stdc++.h>
using namespace std;
const int maxn = 2e5+100;
int n;
int a[maxn];
int get(int x){return x&(-x);}
void updata(int x){while(x<=n){a[x]++,x+=get(x);}}
int sum(int x){int res = 0;while(x>0){res+=a[x],x-=get(x);}return res;}
int ss[maxn],tt[maxn],rk[maxn];
int main()
{
    long long ans = 0;
    memset(a,0,sizeof(a));
    cin>>n;
    for(int i=1;i<=n;i++)scanf("%d",&ss[i]);
    for(int i=1;i<=n;i++)scanf("%d",&tt[i]);
    for(int i=1;i<=n;i++)rk[tt[i]] = i;
    for(int i=1;i<=n;i++)tt[i] = rk[ss[i]];
    for(int i=1;i<=n;i++){ans+=(long long)(i-1-sum(tt[i]));updata(tt[i]);}
    cout<<ans<<endl;
    return 0;
}