add string hashing

Author: lrvideckis

library/strings/string_hash.hpp

@@ -0,0 +1,27 @@
+#pragma once
+//! https://codeforces.com/blog/entry/4898#comment-157965
+//! - use random base to avoid getting hacked on codeforces
+//! - work mod 1e9+7 if birthday paradox is not a problem
+//! @time O(n + q)
+//! @space O(n)
+using mint = array<ll, 2>;
+constexpr mint mod = {ll(1e9 + 7), ll(1e9 + 9)};
+const ll base = 239017;
+struct str_hash {
+  vector<mint> ha, pw;
+  str_hash(const auto& s): ha(sz(s) + 1), pw(ha) {
+    pw[0] = {1, 1};
+    rep(i, 0, sz(s)) rep(j, 0, 2) {
+      pw[i + 1][j] = pw[i][j] * base % mod[j];
+      ha[i + 1][j] = (ha[i][j] * base + s[i] + 1) % mod[j];
+    }
+  }
+  mint subarray(int l, int r) { // [l, r)
+    mint res;
+    rep(j, 0, 2) {
+      res[j] = ha[r][j] - ha[l][j] * pw[r - l][j] % mod[j];
+      if (res[j] < 0) res[j] += mod[j];
+    }
+    return res;
+  }
+};

tests/library_checker_aizu_tests/strings/hashing_lib_checker_z_alg.test.cpp

@@ -0,0 +1,24 @@
+#define PROBLEM \
+  "https://judge.yosupo.jp/problem/zalgorithm"
+#include "../template.hpp"
+#include "../../../library/strings/string_hash.hpp"
+int main() {
+  cin.tie(0)->sync_with_stdio(0);
+  string s;
+  cin >> s;
+  int n = sz(s);
+  str_hash hash(s);
+  for (int i = 0; i < n; i++) {
+    int start = i, end = n + 1;
+    while (start + 1 < end) {
+      int mid = (start + end) / 2;
+      int len = mid - i;
+      if (hash.subarray(i, mid) == hash.subarray(0, len))
+        start = mid;
+      else end = mid;
+    }
+    cout << start - i << ' ';
+  }
+  cout << '\n';
+  return 0;
+}