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Hash (range).cpp
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Hash (range).cpp
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int pw1[N], pw2[N], inv1[N], inv2[N];
int mul(int a, int b) {
a = ((a % mod) + mod) % mod;
b = ((b % mod) + mod) % mod;
return (a * 1LL * b) % mod;
}
int add(int a, int b) {
a = ((a % mod) + mod) % mod;
b = ((b % mod) + mod) % mod;
return (a + b) % mod;
}
int fastPower(int base, int power) {
if (!power) return 1;
int ret = fastPower(base, power >> 1);
ret = mul(ret, ret);
if (power % 2) ret = mul(ret, base);
return ret;
}
void pre() {
pw1[0] = inv1[0] = pw2[0] = inv2[0] = 1;
int mulInv1 = fastPower(P1, mod - 2);
int mulInv2 = fastPower(P2, mod - 2);
for (int i = 1; i < N; i++) {
pw1[i] = mul(pw1[i - 1], P1);
pw2[i] = mul(pw2[i - 1], P2);
inv1[i] = mul(inv1[i - 1], mulInv1);
inv2[i] = mul(inv2[i - 1], mulInv2);
}
}
struct RangeHash {
vector<pii > prefixHash;
RangeHash(string &s) {
prefixHash = vector<pii >(s.size(), {0, 0});
for (int i = 0; i < s.size(); i++) {
prefixHash[i].F = mul(s[i] - 'a' + 1, pw1[i]);
prefixHash[i].S = mul(s[i] - 'a' + 1, pw2[i]);
if (i) {
prefixHash[i] = {
add(prefixHash[i].F, prefixHash[i - 1].F),
add(prefixHash[i].S, prefixHash[i - 1].S)
};
}
}
}
pii getHashVal() {
return prefixHash.back();
}
pii getRangeHashVal(int l, int r) {
return {
mul(add(prefixHash[r].F, -(l ? prefixHash[l - 1].F : 0)), inv1[l]),
mul(add(prefixHash[r].S, -(l ? prefixHash[l - 1].S : 0)), inv2[l])
};
}
};