BZOJ 2084 二分+hash OR Manacher

思路：

二分+哈希

//By SiriusRen
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long ll;
const int N=500050;
const ll mod=1000000007;
int n;
ll hs1[N],hs2[N],base[N],Ans;
char s1[N],s2[N];
int main(){
    scanf("%d",&n);
    scanf("%s",s1+1),base[0]=1;
    for(int i=1;i<=n;i++)
        hs1[i]=(hs1[i-1]*50+s1[i])%mod,
        s2[i]=s1[i]==‘1‘?‘0‘:‘1‘,base[i]=base[i-1]*50%mod;
    for(int i=n;i;i--)hs2[i]=(hs2[i+1]*50+s2[i])%mod;
    for(int i=1;i<n;i++){
        int l=0,r=min(n-i,i),ans=0;
        while(l<=r){
            int mid=(l+r)>>1;
            if(((hs1[i]-hs1[i-mid]*base[mid]%mod)+mod)%mod==((hs2[i+1]-hs2[i+mid+1]*base[mid]%mod)+mod)%mod)
                l=mid+1,ans=mid;
            else r=mid-1;
        }
        Ans+=ans;
    }printf("%lld\n",Ans);
}

Manacher改一下条件

0只能匹配1  1只能匹配0 #匹配#

（长度从0开始匹配  这样就相当于只能从#开始走了 也就是长度为偶数）

//By SiriusRen
#include <cstdio>
#include <algorithm>
using namespace std;
typedef long long ll;
const int N=1000050;
ll ans;
int n,p[N];
char s[N],ch[N];
bool cmp(char x,char y){return (x==‘#‘&&y==‘#‘)||(x==‘1‘&&y==‘0‘)||(x==‘0‘&&y==‘1‘);}
void Manacher(){
    int mx=0,id=0;
    for(int i=1;i<=n;i++){
        if(mx>i)p[i]=min(p[id*2-i],p[id]+id-i);
        else p[i]=0;
        while(cmp(s[i-p[i]],s[i+p[i]]))p[i]++;
        if(i+p[i]>mx)mx=i+p[i],id=i;
        ans+=p[i]/2;
    }
}
int main(){
    scanf("%d",&n);
    scanf("%s",ch+1);
    s[1]=‘#‘;
    for(int i=1;i<=n;i++)s[i<<1]=ch[i],s[i<<1|1]=‘#‘;
    n=n<<1|1;Manacher();
    printf("%lld\n",ans);
}