Editorial for Tiền tố và hậu tố


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Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

Code mẫu của happyboy99x

#include<cstdio>
#include<cstring>

#define N 100005
#define MOD 1000000007LL
typedef long long LL;

char a[N], b[N];
int n, m;
LL hashA[N], pow[N], hashB[N];

void init() {
    hashA[0] = 0; hashB[0] = 0; pow[0] = 1;
    for(int i = 1; i <= n; ++i) hashA[i] = (hashA[i-1] * 26 + a[i] - 'a') % MOD;
    for(int i = 1; i <= m; ++i) hashB[i] = (hashB[i-1] * 26 + b[i] - 'a') % MOD;
    for(int i = 1, _n = n > m ? n : m; i <= _n; ++i) pow[i] = (pow[i-1] * 26) % MOD;
}

inline LL getHashA(int i, int j) {
    return (hashA[j] - hashA[i-1] * pow[j-i+1] + MOD * MOD) % MOD;
}

inline LL getHashB(int i, int j) {
    return (hashB[j] - hashB[i-1] * pow[j-i+1] + MOD * MOD) % MOD;
}

int main() {
    scanf("%s%s", a+1, b+1); n = strlen(a+1); m = strlen(b+1);
    init();
    for(int i = n>=m ? n-m+1 : 1, j = n>=m ? m : n; i<=n&&j>0; ++i, --j) 
        if(getHashA(i, n) == getHashB(1, j)) {
            printf("%s%s\n", a+1, b+j+1);
            return 0;
        }
    printf("%s%s\n", a+1, b+1);
    return 0;
}

Code mẫu của ladpro98

program c11str2;//hash
uses    math;
const   base=trunc(1e7)+7;
        fi='';
        maxN=100005;
var     a,b:ansistring;
        na,nb,res:longint;
        pow:array[0..maxN] of longint;
procedure input;
var     inp:text;
begin
        assign(inp,fi);
        reset(inp);
        readln(inp,a);
        readln(inp,b);
        close(inp);
        res:=0;
end;

procedure init;
var     i:longint;
begin

        na:=length(a);
        nb:=length(b);
        pow[0]:=1;
        for i:=1 to max(na,nb) do
        pow[i]:=(26*pow[i-1]) mod base;
end;

procedure hash;
var     i,oa,hashA,hashB:longint;

begin
        oa:=ord('a');
        hashA:=0;
        hashB:=0;
        for i:=1 to min(na,nb) do
        begin
                hashA:=((ord(a[na-i+1])-oa)*pow[i-1]+hashA) mod base;
                hashB:=(26*hashB+ord(b[i])-oa) mod base;
                if (hashA=hashB) then
                res:=i;
        end;
end;

procedure output;
begin
        write(copy(a,1,na-res));
        write(b);
end;

begin
        input;
        init;
        hash;
        output;
end.

Code mẫu của RR

#include <sstream>
#include <iomanip>
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <string>
#include <deque>
#include <complex>

#define FOR(i,a,b) for(int i=(a),_b=(b); i<=_b; i++)
#define FORD(i,a,b) for(int i=(a),_b=(b); i>=_b; i--)
#define REP(i,a) for(int i=0,_a=(a); i<_a; i++)
#define FORN(i,a,b) for(int i=(a),_b=(b);i<_b;i++)
#define DOWN(i,a,b) for(int i=a,_b=(b);i>=_b;i--)
#define SET(a,v) memset(a,v,sizeof(a))
#define sqr(x) ((x)*(x))
#define ll long long
#define F first
#define S second
#define PB push_back
#define MP make_pair

#define DEBUG(x) cout << #x << " = "; cout << x << endl;
#define PR(a,n) cout << #a << " = "; FOR(_,1,n) cout << a[_] << ' '; cout << endl;
#define PR0(a,n) cout << #a << " = "; REP(_,n) cout << a[_] << ' '; cout << endl;
using namespace std;

//Buffer reading
int INP,AM,REACHEOF;
#define BUFSIZE (1<<12)
char BUF[BUFSIZE+1], *inp=BUF;
#define GETCHAR(INP) { \
    if(!*inp) { \
        if (REACHEOF) return 0;\
        memset(BUF,0,sizeof BUF);\
        int inpzzz = fread(BUF,1,BUFSIZE,stdin);\
        if (inpzzz != BUFSIZE) REACHEOF = true;\
        inp=BUF; \
    } \
    INP=*inp++; \
}
#define DIG(a) (((a)>='0')&&((a)<='9'))
#define GN(j) { \
    AM=0;\
    GETCHAR(INP); while(!DIG(INP) && INP!='-') GETCHAR(INP);\
    if (INP=='-') {AM=1;GETCHAR(INP);} \
    j=INP-'0'; GETCHAR(INP); \
    while(DIG(INP)){j=10*j+(INP-'0');GETCHAR(INP);} \
    if (AM) j=-j;\
}
//End of buffer reading

const long double PI = acos((long double) -1.0);

const int MN = 100111;

long long ha[MN], hb[MN], p[MN];
char a[MN], b[MN];
int la, lb;

bool check(int common) {
    int starta = la - common;
    long long h1;
    if (starta == 0) h1 = ha[la-1];
    else h1 = ha[la-1] - ha[starta-1];

    long long h2 = hb[common-1] * p[la-common];

    return h1 == h2;
}

int main() {
    gets(a); gets(b);
    la = strlen(a), lb = strlen(b);
    p[0] = 1;
    FOR(i,1,100000) p[i] = p[i-1] * 31;

    REP(i,la) {
        if (i) ha[i] = ha[i-1];
        ha[i] += (a[i] - 'a' + 1) * p[i];
    }

    REP(i,lb) {
        if (i) hb[i] = hb[i-1];
        hb[i] += (b[i] - 'a' + 1) * p[i];
    }

    FORD(common,min(la, lb), 1) {
        if (check(common)) {
            REP(i,la) putchar(a[i]);
            FOR(i,common,lb-1) putchar(b[i]);
            puts("");
            return 0;
        }
    }
    REP(i,la) putchar(a[i]);
    REP(i,lb) putchar(b[i]);
    puts("");
    return 0;
}

Code mẫu của hieult

#include <set>
#include <map>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <cassert>
#include <cstdlib>
#include <cstring>
#include <sstream>
#include <iomanip>
#include <iostream>
#include <algorithm>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef unsigned int ui;
typedef unsigned long long ull;

#define Rep(i,n) for(typeof(n) i = 0; i < (n); ++i)
#define Repd(i,n) for(typeof(n) i = (n)-1; i >= 0; --i)
#define For(i,a,b) for(typeof(b) i = (a); i <= (b); ++i)
#define Ford(i,a,b) for(typeof(a) i = (a); i >= (b); --i)
#define Fit(i,v) for(typeof((v).begin()) i = (v).begin(); i != (v).end(); ++i)
#define Fitd(i,v) for(typeof((v).rbegin()) i = (v).rbegin(); i != (v).rend(); ++i)
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define sz(a) ((int)(a).size())
#define all(a) (a).begin(), (a).end()
#define ms(a,x) memset(a, x, sizeof(a))
#define nl puts("")
#define sp printf(" ")
#define ok puts("ok")
//#include <conio.h>

template<class F, class T> T convert(F a, int p = -1) { stringstream ss; if (p >= 0) ss << fixed << setprecision(p); ss << a; T r; ss >> r; return r; }
template<class T> void db(T a, int p = -1) { if (p >= 0) cout << fixed << setprecision(p); cout << a << " "; }
template<class T> T gcd(T a, T b) { T r; while (b != 0) { r = a % b; a = b; b = r; } return a; }
template<class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
template<class T> T sqr(T x) { return x * x; }
template<class T> T cube(T x) { return x * x * x; }
template<class T> struct Triple { T x, y, z; Triple() {} Triple(T _x, T _y, T _z) : x(_x), y(_y), z(_z) {} };
template<class T> Triple<T> euclid(T a, T b) { if (b == 0) return Triple<T>(1, 0, a); Triple<T> r = euclid(b, a % b); return Triple<T>(r.y, r.x - a / b * r.y, r.z); }
template<class T> int getbit(T s, int i) { return (s >> i) & 1; }
template<class T> T onbit(T s, int i) { return s | (T(1) << i); }
template<class T> T offbit(T s, int i) { return s & (~(T(1) << i)); }
template<class T> int cntbit(T s) { return s == 0 ? 0 : cntbit(s >> 1) + (s & 1); }
const int bfsz = 1 << 16; char bf[bfsz + 5]; int rsz = 0;int ptr = 0;
char gc() { if (rsz <= 0) { ptr = 0; rsz = fread(bf, 1, bfsz, stdin); if (rsz <= 0) return EOF; } --rsz; return bf[ptr++]; }
void ga(char &c) { c = EOF; while (!isalpha(c)) c = gc(); }
int gs(char s[]) { int l = 0; char c = gc(); while (isspace(c)) c = gc(); while (c != EOF && !isspace(c)) { s[l++] = c; c = gc(); } s[l] = '\0'; return l; }
template<class T> bool gi(T &v) {
    v = 0; char c = gc(); while (c != EOF && c != '-' && !isdigit(c)) c = gc(); if (c == EOF) return false; bool neg = c == '-'; if (neg) c = gc();
    while (isdigit(c)) { v = v * 10 + c - '0'; c = gc(); } if (neg) v = -v; return true;
}

const double PI = 2 * acos(0);
const string months[] = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
const int days[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
const int dr[] = {0, +1, 0, -1};
const int dc[] = {+1, 0, -1, 0};
const int inf = (int)1e9 + 5;
const ll linf = (ll)1e16 + 5;
const ld eps = 1e-9;
const ll mod = 100000007;
typedef pair<int, int> II;

#define maxn 100005
#define maxe 100005

string a, b, c;

int main() {
//    freopen("in.txt", "r", stdin);
//    freopen("out.txt", "w", stdout);
    cin >> a >> b;
    int lena = a.length(), lenb = b.length();
    int n = min(lena, lenb);
    ll hasha = 0, hashb = 0, mul = 1, res = 0;
    For(i, 1, n){
        hasha += mul * (a[lena - i] - 'a');
        hashb = hashb * 27 + (b[i - 1] - 'a');
        mul *= 27;
       // cout << hasha << "  " << hashb << endl;
        if(hasha == hashb) res = i;
    }
    c = a.substr(0, lena - res) + b;
    cout << c;
}

Code mẫu của skyvn97

#include<stdio.h>
#include<string.h>
#define MAX   100100
#define BASE   26
using namespace std;
typedef long long ll;
char a[MAX];
char b[MAX];
const ll mod[]={1e9+7,1e9+9,1e9+21,1e9+33};
ll p[4][MAX];
ll sa[4][MAX];
ll sb[4][MAX];
int m,n;
int max(int x,int y) {
    if (x>y) return (x); else return (y);
}
void init(void) {
    scanf("%s",a);
    scanf("%s",b);
    m=strlen(a);
    n=strlen(b);
    int i,j;
    for (i=0;i<4;i=i+1) {
        p[i][0]=1;
        sa[i][0]=0;
        sb[i][0]=0;
        for (j=1;j<=max(m,n);j=j+1) p[i][j]=(p[i][j-1]*BASE)%mod[i];
        for (j=1;j<=m;j=j+1) sa[i][j]=(sa[i][j-1]+(a[j-1]-'a')*p[i][j-1])%mod[i];
        for (j=1;j<=n;j=j+1) sb[i][j]=(sb[i][j-1]+(b[j-1]-'a')*p[i][j-1])%mod[i];       
    }   
}
bool same(int x) {
    if (x==0) return (true);
    int i;
    ll y,z;
    for (i=0;i<4;i=i+1) {
        y=sa[i][m]-sa[i][m-x];
        z=(sb[i][x]*p[i][m-x])%mod[i];
        if ((y-z)%mod[i]!=0) return (false);
    }
    return (true);
}
void process(void) {
    int i,j;
    for (i=m+n-max(m,n);i>=0;i=i-1)
        if (same(i)) break;
    j=i;    
    printf("%s",a);
    for (i=j;i<n;i=i+1) printf("%c",b[i]);
}
int main(void) {
    init();
    process();
}

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