字符串哈希

字符串哈希前缀和

ULL get(int l, int r)
{
    return h[r] - h[l - 1] * p[r - l + 1];
}
int main()
{
    cin >> n >> m >> str + 1;
    p[0] = 1;
    for(int i = 1; i <= n; i ++ ){
        p[i] = p[i - 1] * P;
        h[i] = h[i - 1] * P + str[i];
    }

普通哈希

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int mod=5009;
struct p{
    int to,nxt;
}d[50009];int head[50009],cnt=1;
bool add(int x)
{
    int now=(x%mod+mod)%mod;
    for(int i=head[now];i;i=d[i].nxt)
        if(d[i].to==x)    return false;
    d[cnt].to=x,d[cnt].nxt=head[now];
    head[now]=cnt++;
    return true;
}
int main()
{
    int t,n;
    cin>>t;
    while(t--)
    {
        cin>>n;
        cnt=1;
        memset(d,0,sizeof(d));memset(head,0,sizeof(head));
        for(int i=1;i<=n;i++)
        {
            int x;scanf("%d",&x);
            if(add(x))    printf("%d ",x);
        }
        cout<<endl;
    }
    return 0;
}

字符串哈希

溢出哈希

#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ull;
ull base=131;//131进制
ull a[10010];//hash后的数组
int n,ans=1;
ull hashs(string s)
{
    int l=s.length();
    ull he=0;
    for(int i=0;i<l;i++)
        ans=ans*base+(ull)s[i];//溢出相当于取模
    return ans&0x7fffffff;    
} 
int main()
{
    scanf("%d",&n);
    string s;
    for(int i=1;i<=n;i++)
    {
        cin>>s;
        a[i]=hashs(s);
    }
    sort(a+1,a+1+n);
    for(int i=2;i<=n;i++)
        if(a[i]!=a[i-1])
            ans++;
    cout<<ans;
}

双模数哈希

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
typedef unsigned long long ull;
ull base=131;
struct data
{
    ull x,y;
}a[10010];
char s[10010];
int n,ans=1;
ull mod1=19260817;
ull mod2=19660813;
ull hash1(char s[])
{
    int len=strlen(s);
    ull ans=0;
    for (int i=0;i<len;i++)
        ans=(ans*base+(ull)s[i])%mod1;
    return ans;
}
ull hash2(char s[])
{
    int len=strlen(s);
    ull ans=0;
    for (int i=0;i<len;i++)
        ans=(ans*base+(ull)s[i])%mod2;
    return ans;
}
bool comp(data a,data b)
{
    return a.x<b.x;
}
main()
{
    scanf("%d",&n);
    for (int i=1;i<=n;i++)
    {
        scanf("%s",s);
        a[i].x=hash1(s);
        a[i].y=hash2(s);
    }
    sort(a+1,a+n+1,comp);
    for (int i=2;i<=n;i++)
        if (a[i].x!=a[i-1].x || a[i-1].y!=a[i].y)
            ans++;
    printf("%d
",ans);
}