Golf (#181)

* Enhance walk function with optimized logic

Refactor walk function to improve performance and clarity.

* Fix boundary condition in segment tree walk

* [auto-verifier] verify commit 3beb2d1

* Fix boundary condition in segment tree walk function

* Fix bug in segment tree walk function

* [auto-verifier] verify commit 267032c

* Update segment tree walk logic with good flag

Refactor segment tree walk function to use a boolean flag for condition checking.

* [auto-verifier] verify commit cc93d62

* Fix loop condition in segment tree walk function

* Fix return statement syntax in walk.hpp

* [auto-verifier] verify commit 3f31866

* Fix loop condition and variable initialization in walk.hpp

* [auto-verifier] verify commit b741e86

* Update walk.hpp

* [auto-verifier] verify commit a837375

* more golf!

* [auto-verifier] verify commit b9c25bc

* Reverse conditions in walk function logic

* Change condition in walk function for sum check

* Fix comment to clarify index search condition

* [auto-verifier] verify commit 6405c5e

* format

* [auto-verifier] verify commit 434c09a

* Fix formatting of if statement in test code

* [auto-verifier] verify commit abdb86b

* format

* [auto-verifier] verify commit 7949f33

---------

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

Author: lrvideckis

.verify-helper/timestamps.remote.json

@@ -43,12 +43,6 @@
 "tests/library_checker_aizu_tests/data_structures/rmq_linear.test.cpp": "2026-01-18 11:15:41 +0000",
 "tests/library_checker_aizu_tests/data_structures/rmq_sparse_table.test.cpp": "2026-01-18 11:15:41 +0000",
 "tests/library_checker_aizu_tests/data_structures/rmq_sparse_table_inc.test.cpp": "2026-01-18 11:15:41 +0000",
-"tests/library_checker_aizu_tests/data_structures/simple_tree.test.cpp": "2026-02-07 20:45:45 +0000",
-"tests/library_checker_aizu_tests/data_structures/simple_tree_inc.test.cpp": "2026-02-05 16:06:35 -0700",
-"tests/library_checker_aizu_tests/data_structures/simple_tree_inc_line.test.cpp": "2026-02-05 16:06:35 -0700",
-"tests/library_checker_aizu_tests/data_structures/simple_tree_inc_walk.test.cpp": "2026-02-05 16:06:35 -0700",
-"tests/library_checker_aizu_tests/data_structures/simple_tree_line.test.cpp": "2026-02-07 20:45:45 +0000",
-"tests/library_checker_aizu_tests/data_structures/simple_tree_walk.test.cpp": "2026-02-07 20:45:45 +0000",
 "tests/library_checker_aizu_tests/flow/dinic_aizu.test.cpp": "2024-11-17 14:04:03 -0600",
 "tests/library_checker_aizu_tests/flow/hungarian.test.cpp": "2024-11-17 14:04:03 -0600",
 "tests/library_checker_aizu_tests/flow/min_cost_max_flow.test.cpp": "2024-12-05 10:41:42 -0600",

library/data_structures_[l,r]/seg_tree.hpp

@@ -13,7 +13,7 @@
 //!     tree st(n, INT_MAX, ranges::min);
 //!     int idx = st.walk(l, r, [&](int value) {
 //!       return value <= x;
-//!     }); // smallest index in [l, r] s.t. f is true
+//!     }); // smallest index in [l, r] s.t. f is false
 //!   }
 //! @endcode
 //! @time O(n + q log n)

library/data_structures_[l,r]/seg_tree_uncommon/walk.hpp

@@ -1,10 +1,8 @@
 int walk(int l, int r, const auto& f) {
-  for (l += n, r += n; l <= r;)
-    if (int u = nxt(l, r); f(s[u])) {
-      while (u < n)
-        if (f(s[2 * u])) u *= 2;
-        else (u *= 2)++;
-      return u - n;
-    }
-  return -1;
+  while (l <= r) {
+    int u = l + n, x = __lg(min(u & -u, r - l + 1));
+    if (f(s[u >> x])) l += 1 << x;
+    else r = l + (1 << x) - 2;
+  }
+  return l;
 }

tests/library_checker_aizu_tests/data_structures/simple_tree_inc_walk.test.cpp

@@ -22,9 +22,10 @@ int main() {
       cout << st.query(k, k) << '\n';
     } else if (type == 3) {
       // returns first element in [k,n-1] such that sum > 0
-      cout << st.walk(k, n - 1, [&](int sum) {
-        return sum > 0;
-      }) << '\n';
+      int idx = st.walk(k, n - 1,
+        [&](int sum) { return sum == 0; });
+      if (idx == n) idx = -1;
+      cout << idx << '\n';
     } else {
       assert(type == 4);
       int total = st.query(0, k);
@@ -33,8 +34,10 @@ int main() {
       } else {
         int pref_sum = 0;
         cout << st.walk(0, k, [&](int sum) {
-          if (pref_sum + sum == total) return 1;
-          pref_sum += sum;
+          if (pref_sum + sum < total) {
+            pref_sum += sum;
+            return 1;
+          }
           return 0;
         }) << '\n';
       }