P3501 [POI2010]ANT-Antisymmetry

题面:https://www.luogu.org/problem/P3501

本题直接hash+暴力,二分对称中心即可.
(自然溢出大法好！！！)
Code:
#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<ctime>
#include<map>
#define ull unsigned long long
using namespace std;
const int N=500005,base=131;
int n,a[N],b[N];
ull fac[N],hash1[N],hash2[N],ans,tot;
string s;
bool check(int pos,int len){
    int l=pos-len+1,r=pos,L=n-pos-len,R=n-pos;
    ull ha1=hash1[r]-hash1[l-1]*fac[len],ha2=hash2[R]-hash2[L]*fac[len];
    if(ha1==ha2){
        return 1;
    }
    return 0;
}
int main(){
    cin>>n>>s;
    for(int i=0;i<s.size();i++){
        a[i+1]=s[i]-'0';
    }
    fac[0]=1;
    for(int i=1;i<=n;i++){
        fac[i]=fac[i-1]*base;
    }
    for(int i=1;i<=n;i++){
        hash1[i]=hash1[i-1]*base+a[i]+1;
    }
    for(int i=1;i<=n;i++){
        b[i]=a[n-i+1]^1;
    }
    for(int i=1;i<=n;i++){
        hash2[i]=hash2[i-1]*base+b[i]+1;
    }
    for(int i=1;i<=n;i++){
        int l=1,r=min(i,n-i);
        tot=0;
        while(l<=r){
            int mid=(l+r)>>1;
            if(check(i,mid)){
                l=mid+1;
                tot=mid;
            }
            else{
                r=mid-1;
            }
        }
        ans+=tot;
    }
    cout<<ans<<endl;
    return 0;
}

P3501 [POI2010]ANT-Antisymmetry

原文：https://www.cnblogs.com/ukcxrtjr/p/11656109.html