哈希

哈希表的插入与查找

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#include <iostream>
#include <cstring>
using namespace std;

const int N=2e5+3;
const int INF=0x3f3f3f3f;

int h[N];

int find(int x)
{
    int k=(x%N+N)%N;
    while(h[k]!=INF && h[k]!=x)
    {
        k++;
        if(k==N) k=0;
    }
    return k;
}
int main()
{
    memset(h,0x3f,sizeof h);
    int n;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        char op;
        int x;
        cin>>op>>x;
        if(op=='I')
        {
            int k=find(x);
            h[k]=x;
        }
        else
        {
            int k=find(x);
            if(h[k]==INF) cout<<"No"<<endl;
            else cout<<"Yes"<<endl;
        }
    }
}

字符串哈希

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#include <iostream>
#include <cstring>
using namespace std;

typedef unsigned long long ULL;//P = 131|13331  Q=2^64，在99%的情况下不会出现冲突
const int N=1e5+10;
int P=131;//p取131|13331
ULL p[N],h[N];

ULL get(int l,int r)
{
    return h[r]-h[l-1]*p[r-l+1];
}

int main()
{
    int n,m;
    cin>>n>>m;

    char s[N];
    cin>>s+1;
    p[0]=1;
    h[0]=0;
    for(int i=1;i<=n;i++)
    {
        p[i]=p[i-1]*P;
        h[i]=h[i-1]*P+s[i];
    }
    while(m--)
    {
        int l1,r1,l2,r2;
        cin>>l1>>r1>>l2>>r2;
        if(get(l1,r1)==get(l2,r2)) puts("Yes");
        else puts("No");
    }
}