zoj 1440 zju

http://www.cppblog.com/menjitianya/archive/2011/04/06/143506.html

关键是如何求最少的交换次数，用到了简单哈希

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
typedef long long lld;
#define lowbit(x) (x&-x)
const int maxn = 100010;
int c[maxn],hash[maxn],val[maxn],a[maxn];
void update(int x,int d){
    for(;x>0;x-=lowbit(x))
        c[x]+=d;
}
int sum(int x){
    lld ans=0;
    for(;x<=maxn;x+=lowbit(x))    ans+=c[x];
    return ans;
}
int main(){
    int n,i,j;
    while(scanf("%d",&n)!=EOF){
        lld ans=0;
        memset(c,0,sizeof(c));
        for(i=1;i<=n;i++){
            scanf("%d",&val[i]);
            a[i]=val[i];
        }
        sort(a+1,a+1+n);
        for(i=1;i<=n;i++) val[i]=upper_bound(a+1,a+n+1,val[i])-(a+1);
        for(i=1;i<=n;i++)     hash[val[i]]=i;
        for(i=1;i<=n;i++){
            ans+=sum(val[i]+1);
            update(val[i],1);
        }
        int swp=0;
        for(i=1;i<=n;i++){
              if(val[i]!=i){
                  swp++;
                  int p=hash[i];
                  int now=val[i];
                  swap(val[p],val[i]);
                  hash[now]=p;
              }
        }
        printf("%d\n%lld\n",swp,ans);
    }
}