題目連結

Description

You want to processe a sequence of n distinct integers by swapping two adjacent sequence elements until the sequence is sorted in ascending order. Then how many times it need. For example, 1 2 3 5 4, we only need one operation : swap 5 and 4.

Input

The input consists of a number of test cases. Each case consists of two lines: the first line contains a positive integer n (n <= 1000); the next line contains a permutation of the n integers from 1 to n.

Output

For each case, output the minimum times need to sort it in ascending order on a single line.

Sample Input

3 1 2 3 4 4 3 2 1

Sample Output

0 6

樹狀陣列求逆序對裸題……5分鐘以內寫完，還算比較熟

#include<cstdio>
#include<cstring>
const int N=1e3+10;
int n,sum[N<<1];
void add(int
 
 x){for(;x<=n;x+=x&-x)sum[x]++;}
int query(int x)
{
    int ret=0;
    for(;x;x-=x&-x)ret+=sum[x];
    return ret;
}
int main()
{
    //freopen("in.txt","r",stdin);
    while(~scanf("%d",&n))
    {
        int ans=0;
        memset(sum,0,sizeof(sum));
        for(int i=1;i<=n;i++)
        {
            int
 
 x;
            scanf("%d",&x);
            ans+=query(n)-query(x-1);
            add(x);
        }
        printf("%d\n",ans);
    }
    return 0;
}

總結

巨水