trying different version of ubuntu for CI

Author: lrvideckis

.github/workflows/programming_team_code_ci.yml

@@ -10,7 +10,8 @@ jobs:
     # https://stackoverflow.com/a/76359456
     strategy:
       fail-fast: false
-    runs-on: ubuntu-latest
+    # https://github.com/actions/runner-images/issues/6709#issuecomment-1441444332
+    runs-on: ubuntu-20.04
     steps:
     - uses: actions/checkout@v1
     - name: Set up Python

library/trees/ladder_decomposition/linear_kth_par.hpp

@@ -26,8 +26,7 @@ template<int KAPPA = 2> struct linear_kth_par {
       t++;
     };
     auto dfs = [&](auto&& self, int v, int p) -> void {
-      st[d[v]] = v;
-      int& l = leaf[v] = v;
+      int& l = leaf[v] = st[d[v]] = v;
       pos[v] = t;
       calc(d[v]);
       for (int u : adj[v])