golf (#174)

* Refactor nxt function for segment tree

* [auto-verifier] verify commit 83667d0

---------

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

Author: lrvideckis

.verify-helper/timestamps.remote.json

@@ -44,8 +44,8 @@
 "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": "2026-01-18 11:15:41 +0000",
-"tests/library_checker_aizu_tests/data_structures/simple_tree_inc.test.cpp": "2026-01-22 19:22:57 -0700",
-"tests/library_checker_aizu_tests/data_structures/simple_tree_inc_line.test.cpp": "2026-01-22 19:22:57 -0700",
+"tests/library_checker_aizu_tests/data_structures/simple_tree_inc.test.cpp": "2026-01-22 19:46:25 -0700",
+"tests/library_checker_aizu_tests/data_structures/simple_tree_inc_line.test.cpp": "2026-01-22 19:46:25 -0700",
 "tests/library_checker_aizu_tests/data_structures/simple_tree_line.test.cpp": "2026-01-18 11:15:41 +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",

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

@@ -11,8 +11,8 @@
 //! @time O(n + q log n)
 //! @space O(n)
 int nxt(int& l, int r) {
-  int x = __lg(min(l & -l, r - l + 1));
-  return exchange(l, l + (1 << x)) >> x;
+  int x = l, y = __lg(min(l & -l, r - l + 1));
+  return l += 1 << y, x >> y;
 }
 template<class T, class F> struct tree {
   int n;