Codeforces #985F: Isomorphic Strings 題解

感覺雖然是edu round的倒數第二題但還蠻簡單的
我們分析那個同構的定義，可以理解爲“該一樣的字符要一樣，該不一樣的字符要不一樣”，那麼對於每一種字符我們想一種辦法來表示他在子串中所有的出現位置（像一張有黑點的紙條），然後看看兩個串能不能配對就好
把一個01串轉換成一個數，我剛開始想的是高精度用2n$2^n$ 表示，然而複雜度是炸的，然後我發現自己蠢了，用字符串哈希就可以了
爲了保險我寫了雙哈希

#include <cstdio>
#include <iostream>
#include <cstring>
#include <string>
#include <cstdlib>
#include <utility>
#include <cctype>
#include <algorithm>
#include <bitset>
#include <set>
#include <map>
#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <cmath>
#define LL long long
#define LB long double
#define x first
#define y second
#define Pair pair<int,int>
#define pb push_back
#define pf push_front
#define mp make_pair
#define LOWBIT(x) x & (-x)
using namespace std;

const int MOD=1e9+7;
const LL LINF=2e16;
const int INF=1e9;
const int magic=348;
const double eps=1e-10;
const double pi=3.14159265;

inline int getint()
{
    char ch;int res;bool f;
    while (!isdigit(ch=getchar()) && ch!='-') {}
    if (ch=='-') f=false,res=0; else f=true,res=ch-'0';
    while (isdigit(ch=getchar())) res=res*10+ch-'0';
    return f?res:-res;
}

char s[200048];
vector<int> pos[48];
int n,q;

const int p1=998244353,p2=1004535809;
const int m1=1e9+7,m2=1e9+9;
LL hsh1[48][200048],hsh2[48][200048],P1[200048],P2[200048];
inline void init_hash()
{
    int i,j;P1[0]=P2[0]=1;
    for (i=1;i<=n;i++) P1[i]=(P1[i-1]*p1)%m1,P2[i]=(P2[i-1]*p2)%m2;
    for (i=1;i<=26;i++)
        for (j=1;j<=n;j++)
        {
            hsh1[i][j]=(hsh1[i][j-1]*p1+(s[j]=='a'+i-1)*3)%m1;
            hsh2[i][j]=(hsh2[i][j-1]*p2+(s[j]=='a'+i-1)*3)%m2;
        }
}

inline LL mod1(LL x) {while (x>=m1) x-=m1;while (x<0) x+=m1;return x;}
inline LL mod2(LL x) {while (x>=m2) x-=m2;while (x<0) x+=m2;return x;}
inline LL gethash1(int type,int left,int right) {return mod1(hsh1[type][right]-(hsh1[type][left-1]*P1[right-left+1])%m1);}
inline LL gethash2(int type,int left,int right) {return mod2(hsh2[type][right]-(hsh2[type][left-1]*P2[right-left+1])%m2);}

LL val1[48],val2[48];

int main ()
{
    n=getint();q=getint();scanf("%s",s+1);
    init_hash();
    int s1,s2,len,i;
    while (q--)
    {
        s1=getint();s2=getint();len=getint();
        bool ans=true;
        memset(val1,0,sizeof(val1));memset(val2,0,sizeof(val2));
        for (i=1;i<=26;i++) val1[i]=gethash1(i,s1,s1+len-1),val2[i]=gethash1(i,s2,s2+len-1);
        sort(val1+1,val1+27);sort(val2+1,val2+27);
        for (i=1;i<=26;i++) if (val1[i]!=val2[i]) ans=false;
        memset(val1,0,sizeof(val1));memset(val2,0,sizeof(val2));
        for (i=1;i<=26;i++) val1[i]=gethash2(i,s1,s1+len-1),val2[i]=gethash2(i,s2,s2+len-1);
        sort(val1+1,val1+27);sort(val2+1,val2+27);
        for (i=1;i<=26;i++) if (val1[i]!=val2[i]) ans=false;
        if (ans) puts("YES"); else puts("NO");
    }
    return 0;
}