【BZOJ】【P2789】【Poi2012】【Letters】【题解】【逆序对】

传送门:http://www.lydsy.com/JudgeOnline/problem.php?id=2789

逆序对,不多说

Code:

#include<bits/stdc++.h>using namespace std;const int maxn=1e6+5;int d[maxn];int p[maxn];deque<int>v[233];char s1[maxn],s2[maxn];int n;#define lowbit(x) (x&-x)int get(int x){int ans=0;while(x)ans+=d[x],x-=lowbit(x);return ans;}void updata(int x,int f){while(x<=n)d[x]+=f,x+=lowbit(x);}int main(){scanf("%d",&n);scanf("%s",s1+1);scanf("%s",s2+1);    for(int i=1;i<=n;i++)          v[s1[i]-'A'].push_back(i);      for(int i=1;i<=n;i++){          p[i]=v[s2[i]-'A'].front();          v[s2[i]-'A'].pop_front();      }long long ans=0;    for(int i=1;i<=n;i++){          ans+=i-get(p[i])-1;          updata(p[i],1);    }cout<<ans<<endl;return 0;}