sa short nits (#176)

* Modify suffix array algorithm to use K-based sorting

Refactor suffix array construction to use a base K for sorting.

* [auto-verifier] verify commit 2ddf97e

* Update suffix array test to include LCP verification

* [auto-verifier] verify commit 711cb9b

* Fix loop range in suffix array test

* Fix condition in suffix array test case

* [auto-verifier] verify commit 2cb9676

* Update suffix_array_short.hpp

* Fix suffix array index handling in LCP calculation

* Fix LCP calculation in suffix array implementation

* Fix lcp calculation in suffix_array_short.hpp

* Update LCP calculation to use min function

* Refactor suffix array sorting and LCP computation

* Improve suffix array comparison handling

Refactor comparison logic to handle -1 case in suffix array.

* Add assertion for index 'a' in suffix array

Add assertion to ensure 'a' is within bounds before accessing 'y'.

* Refactor conditionals for clarity in suffix_array_short.hpp

* Update suffix_array_short.hpp

* fix

* [auto-verifier] verify commit 8fd2384

* fix

* nameing nit

* fixes

* copy change here too

* fix

---------

Co-authored-by: GitHub <noreply@github.com>

Author: lrvideckis

.verify-helper/timestamps.remote.json

@@ -106,7 +106,6 @@
 "tests/library_checker_aizu_tests/monotonic_stack_related/count_rectangles.test.cpp": "2026-01-18 11:15:41 +0000",
 "tests/library_checker_aizu_tests/monotonic_stack_related/max_rect_histogram.test.cpp": "2026-01-18 11:15:41 +0000",
 "tests/library_checker_aizu_tests/strings/kmp.test.cpp": "2025-08-05 19:19:23 -0600",
-"tests/library_checker_aizu_tests/strings/lcp_array.test.cpp": "2025-08-05 19:19:23 -0600",
 "tests/library_checker_aizu_tests/strings/lcp_query_palindrome.test.cpp": "2026-01-18 11:15:41 +0000",
 "tests/library_checker_aizu_tests/strings/lcp_query_zfunc.test.cpp": "2026-01-18 11:15:41 +0000",
 "tests/library_checker_aizu_tests/strings/lcs_dp.test.cpp": "2025-08-05 19:19:23 -0600",
@@ -119,7 +118,6 @@
 "tests/library_checker_aizu_tests/strings/sa_sort_pairs.test.cpp": "2026-01-18 11:15:41 +0000",
 "tests/library_checker_aizu_tests/strings/single_matching_bs.test.cpp": "2026-01-18 11:15:41 +0000",
 "tests/library_checker_aizu_tests/strings/suffix_array.test.cpp": "2026-01-18 11:15:41 +0000",
-"tests/library_checker_aizu_tests/strings/suffix_array_short.test.cpp": "2025-08-05 19:19:23 -0600",
 "tests/library_checker_aizu_tests/strings/trie.test.cpp": "2026-01-17 12:38:18 -0700",
 "tests/library_checker_aizu_tests/strings/wildcard_pattern_matching.test.cpp": "2025-08-05 19:19:23 -0600",
 "tests/library_checker_aizu_tests/trees/count_paths_per_length.test.cpp": "2025-12-11 21:47:53 +0000",

library/strings/suffix_array/suffix_array.hpp

@@ -57,14 +57,13 @@ auto get_sa(const auto& s, int max_num) {
     }
     if (max_num == n) break;
   }
-  int sz = 0;
+  int l = 0;
   rep(i, 0, n) {
-    if (sz > 0) sz--;
+    if (l > 0) l--;
     if (sa_inv[i] == 0) continue;
-    for (int j = sa[sa_inv[i] - 1];
-      max(i, j) + sz < n && s[i + sz] == s[j + sz];)
-      sz++;
-    lcp[sa_inv[i] - 1] = sz;
+    int j = sa[sa_inv[i] - 1];
+    while (max(i, j) + l < n && s[i + l] == s[j + l]) l++;
+    lcp[sa_inv[i] - 1] = l;
   }
   return tuple{sa, sa_inv, lcp};
 }

library/strings/suffix_array/suffix_array_short.hpp

@@ -7,31 +7,35 @@
 //!   vi s_vec;
 //!   auto [sa1, sa_inv1, lcp1] = sa_short(s_vec);
 //! @endcode
-//! runs in ~1.5s for 5e5
+//! runs in ~0.5s for 5e5
 //! @time O(n * log^2(n))
 //! @space O(n)
 auto sa_short(const auto& s) {
-  int n = sz(s);
+  const int n = sz(s), b = 6;
   vi sa(n), sa_inv(all(s)), lcp(n - 1);
   iota(all(sa), 0);
-  for (int k = 1; k <= n; k *= 2) {
+  for (int j = 1; j <= n; j *= b) {
     vi x(sa_inv);
-    auto proj = [&](int i) {
-      return pair(x[i], i + k < n ? x[i + k] : -1);
+    auto cmp = [&](int i1, int i2) {
+      rep(k, 0, b) {
+        int a = i1 + j * k < n ? x[i1 + j * k] : -1;
+        int b = i2 + j * k < n ? x[i2 + j * k] : -1;
+        if (a != b) return a < b;
+      }
+      return false;
     };
-    ranges::sort(sa, {}, proj);
+    sort(all(sa), cmp);
     sa_inv[sa[0]] = 0;
     rep(i, 1, n) sa_inv[sa[i]] =
-      sa_inv[sa[i - 1]] + (proj(sa[i - 1]) != proj(sa[i]));
+      sa_inv[sa[i - 1]] + cmp(sa[i - 1], sa[i]);
   }
-  int sz = 0;
+  int l = 0;
   rep(i, 0, n) {
-    if (sz > 0) sz--;
+    if (l > 0) l--;
     if (sa_inv[i] == 0) continue;
-    for (int j = sa[sa_inv[i] - 1];
-      max(i, j) + sz < n && s[i + sz] == s[j + sz];)
-      sz++;
-    lcp[sa_inv[i] - 1] = sz;
+    int j = sa[sa_inv[i] - 1];
+    while (max(i, j) + l < n && s[i + l] == s[j + l]) l++;
+    lcp[sa_inv[i] - 1] = l;
   }
   return tuple{sa, sa_inv, lcp};
 }

tests/.config/.cppcheck_suppression_list

@@ -40,7 +40,7 @@ syntaxError:../library/loops/supermasks.hpp:8
 syntaxError:../library/math/prime_sieve/mobius.hpp:6
 syntaxError:../library/trees/lca_rmq/iterate_subtree.hpp:6
 knownConditionTrueFalse:../library/strings/suffix_array/suffix_array.hpp:62
-knownConditionTrueFalse:../library/strings/suffix_array/suffix_array_short.hpp:29
+knownConditionTrueFalse:../library/strings/suffix_array/suffix_array_short.hpp:34
 knownConditionTrueFalse:../library/dsu/kruskal_tree.hpp:15
 knownConditionTrueFalse:../library/dsu/dsu.hpp:11
 constVariable:../kactl/content/numerical/NumberTheoreticTransform.h:30

tests/library_checker_aizu_tests/strings/suffix_array_short.test.cpp

@@ -9,11 +9,22 @@ int main() {
   cin.tie(0)->sync_with_stdio(0);
   string s;
   cin >> s;
-  auto [sa, sa_inv, _] = sa_short(vi(all(s)));
-  for (int i = 0; i < sz(s); i++) {
+  auto [sa, sa_inv, lcp] = sa_short(vi(all(s)));
+  rep(i, 0, sz(s)) {
     assert(sa[sa_inv[i]] == i);
     assert(sa_inv[sa[i]] == i);
   }
+  vi lcp_kasai(sz(s) - 1);
+  int sz = 0;
+  rep(i, 0, sz(s)) {
+    if (sz > 0) sz--;
+    if (sa_inv[i] == 0) continue;
+    for (int j = sa[sa_inv[i] - 1];
+      max(i, j) + sz < sz(s) && s[i + sz] == s[j + sz];)
+      sz++;
+    lcp_kasai[sa_inv[i] - 1] = sz;
+  }
+  assert(lcp == lcp_kasai);
   for (int val : sa) cout << val << " ";
   cout << '\n';
 }

tests/scripts/grep_clangformat_cppcheck.sh

@@ -16,9 +16,6 @@ grep --extended-regexp "template\s?<typename" --recursive ../library/ && exit 1
 echo "check 1 instead of true"
 grep "true" --recursive ../library/ && exit 1
 
-echo "check 0 instead of false"
-grep "false" --recursive ../library/ && exit 1
-
 echo "check ll instead of long long or int64_t"
 grep "long long" --recursive ../library/ && exit 1
 grep "int64_t" --recursive ../library/**/*.hpp | grep "uint64_t" --invert-match && exit 1