make it work in debug mode

Author: lrvideckis

library/data_structures_[l,r)/uncommon/priority_queue_of_updates.hpp

@@ -29,8 +29,8 @@ template<class F, class G> struct pq_updates {
     int l = sz(st), r = l;
     for (auto& [_, i] : mp) {
       l = min(l, i);
-      swap(st[i], st[--r]);
-      swap(st[i].first->second, i);
+      if (i != --r)
+        swap(st[i], st[r]), swap(st[i].first->second, i);
       if (r - l <= sz(st) - r) break;
     }
     rep(i, l, sz(st)) undo();

tests/library_checker_aizu_tests/handmade_tests/pq_updates.test.cpp

@@ -1,8 +1,5 @@
 #define PROBLEM \
   "https://onlinejudge.u-aizu.ac.jp/problems/ITP1_1_A"
-// swapping iterators in as part of `swap(st[i], st[--r]);`
-// leads to RTE with debug mode :(
-#undef _GLIBCXX_DEBUG
 #include "../template.hpp"
 #include "../../../library/contest/random.hpp"
 #include "../../../library/data_structures_[l,r)/uncommon/priority_queue_of_updates.hpp"