「LibreOJ NOIP Round #1」537 DNA 序列

 

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#include <iostream>
#include <map>
#include <cstring>
#include <cstdio>
using namespace std;
typedef unsigned long long ULL;
map<ULL, int>Cnt;
const int maxn = 5e6 + 7;
ULL h[maxn], p[maxn];
int base = 3;
char s[maxn];
int k;

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

int main()
{
    scanf("%s%d",s+1,&k);

    p[0] = 1;
    int len = strlen(s+1);
    for(int i = 1; i <= len; i++)
    {
        p[i] = p[i-1]*base;
        h[i] = h[i-1]*base + s[i];
        if(i >= k)
        {
            ULL tmp = get(i-k+1,i);
            Cnt[tmp]++;
        }
    }
    int ans = 0;
    for(map<ULL,int>::iterator it = Cnt.begin() ; it != Cnt.end() ; ++it) ans = max(ans,it->second);
    printf("%d
",ans);
    return 0;
}