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1. Rabin_carp.cpp
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1. Rabin_carp.cpp
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#include<bits/stdc++.h>
#define int long long int
using namespace std;
const int p = 31, mod = 1e9 + 7;
int poly_hash(string s) {
int hash = 0;
int p_power = 1;
for (int i = 0; i < s.size(); i++) {
hash += (s[i] - 'a' + 1) * p_power;
p_power *= p;
hash %= mod;
p_power %= mod;
}
return hash;
}
int powr(int a, int b) {
// (a^b)%mod
int res = 1;
while (b) {
if (b & 1) res *= a;
b /= 2;
a *= a;
a %= mod;
res %= mod;
}
return res;
}
int inv(int x) {
return powr(x, mod - 2);
}
int32_t main() {
#ifndef ONLINE_JUDGE
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
string text = "ababbabbaba";
string pattern = "aba";
int pat_hash = poly_hash(pattern);
int n = text.size(), m = pattern.size();
int text_hash = poly_hash(text.substr(0, m));
if (pat_hash == text_hash) {
cout << 0 << '\n';
}
for (int i = 1; i + m <= n; i++) {
// remove last character
text_hash = (text_hash - (text[i - 1] - 'a' + 1) + mod) % mod;
text_hash = (text_hash * inv(p)) % mod;
text_hash = (text_hash + (text[i + m - 1] - 'a' + 1) * powr(p, m - 1)) % mod;
// cout << pat_hash << " " << text_hash << '\n';
if (text_hash == pat_hash) {
cout << i << '\n';
}
}
return 0;
}