feat(codeforces/970): a-f

codeforces/970/.clang-format

@@ -0,0 +1,9 @@
+BasedOnStyle: Google
+AllowShortBlocksOnASingleLine: false
+AllowShortCaseLabelsOnASingleLine: false
+AllowShortCompoundRequirementOnASingleLine: false
+AllowShortEnumsOnASingleLine: false
+AllowShortFunctionsOnASingleLine: false
+AllowShortIfStatementsOnASingleLine: false
+AllowShortLambdasOnASingleLine: false
+AllowShortLoopsOnASingleLine: false

codeforces/970/.clangd

@@ -0,0 +1,34 @@
+CompileFlags:
+	Add:
+		-O2
+		-Wall
+		-Wextra
+		-Wpedantic
+		-Wshadow
+		-Wformat=2
+		-Wfloat-equal
+		-Wlogical-op
+		-Wshift-overflow=2
+		-Wnon-virtual-dtor
+		-Wold-style-cast
+		-Wcast-qual
+		-Wuseless-cast
+		-Wno-sign-promotion
+		-Wcast-align
+		-Wunused
+		-Woverloaded-virtual
+		-Wconversion
+		-Wsign-conversion
+		-Wmisleading-indentation
+		-Wduplicated-cond
+		-Wduplicated-branches
+		-Wlogical-op
+		-Wnull-dereference
+		-Wformat=2
+		-Wformat-overflow
+		-Wformat-truncation
+		-Wdouble-promotion
+		-Wundef
+		-DLOCAL
+		-std=c++20
+		-Wno-unknown-pragmas

codeforces/970/a.cc

@@ -0,0 +1,87 @@
+#include <bits/stdc++.h>  // {{{
+
+// https://codeforces.com/blog/entry/96344
+
+#pragma GCC optimize("O2,unroll-loops")
+#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
+
+using namespace std;
+
+using i32 = int32_t;
+using u32 = uint32_t;
+using i64 = int64_t;
+using u64 = uint64_t;
+using d64 = double;
+using d128 = long double;
+template <typename T>
+using vec = std::vector<T>;
+template <typename T, size_t N>
+using arr = std::array<T, N>;
+template <typename T1, typename T2>
+using pai = std::pair<T1, T2>;
+
+template <typename T>
+constexpr T MIN = std::numeric_limits<T>::min();
+
+template <typename T>
+constexpr T MAX = std::numeric_limits<T>::max();
+
+template <typename T>
+[[nodiscard]] static T sc(auto&& x) {
+  return static_cast<T>(x);
+}
+
+template <typename T>
+[[nodiscard]] static T sz(auto&& x) {
+  return static_cast<T>(x.size());
+}
+
+static void NO() {
+  std::cout << "NO\n";
+}
+
+static void YES() {
+  std::cout << "YES\n";
+}
+
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+
+#ifdef LOCAL
+#define db(...) std::print(__VA_ARGS__)
+#define dbln(...) std::println(__VA_ARGS__)
+#else
+#define db(...)
+#define dbln(...)
+#endif
+//  }}}
+
+void solve() {
+  u32 ones, twos;
+  cin >> ones >> twos;
+
+  for (u32 c1 = 0; c1 <= ones; ++c1) {
+    for (u32 c2 = 0; c2 <= twos; ++c2) {
+      if (c1 + c2 * 2 == (ones - c1) + (twos - c2) * 2) {
+        YES();
+        return;
+      }
+    }
+  }
+  NO();
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+  cin.exceptions(cin.failbit);
+
+  int tc = 1;
+  cin >> tc;
+
+  for (int t = 0; t < tc; ++t) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}

codeforces/970/b.cc

@@ -0,0 +1,130 @@
+#include <bits/stdc++.h>  // {{{
+
+// https://codeforces.com/blog/entry/96344
+
+#pragma GCC optimize("O2,unroll-loops")
+#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
+
+using namespace std;
+
+using i32 = int32_t;
+using u32 = uint32_t;
+using i64 = int64_t;
+using u64 = uint64_t;
+using d64 = double;
+using d128 = long double;
+template <typename T>
+using vec = std::vector<T>;
+template <typename T, size_t N>
+using arr = std::array<T, N>;
+template <typename T1, typename T2>
+using pai = std::pair<T1, T2>;
+
+template <typename T>
+constexpr T MIN = std::numeric_limits<T>::min();
+
+template <typename T>
+constexpr T MAX = std::numeric_limits<T>::max();
+
+template <typename T>
+[[nodiscard]] static T sc(auto&& x) {
+  return static_cast<T>(x);
+}
+
+template <typename T>
+[[nodiscard]] static T sz(auto&& x) {
+  return static_cast<T>(x.size());
+}
+
+static void NO() {
+  std::cout << "No\n";
+}
+
+static void YES() {
+  std::cout << "Yes\n";
+}
+
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+
+#ifdef LOCAL
+#define db(...) std::print(__VA_ARGS__)
+#define dbln(...) std::println(__VA_ARGS__)
+#else
+#define db(...)
+#define dbln(...)
+#endif
+//  }}}
+
+void solve() {
+  u32 n;
+  string s;
+  cin >> n >> s;
+
+  i64 cols = -1;
+  for (u32 i = 0; i < n; ++i) {
+    if (s[i] == '0') {
+      cols = i - 1;
+      break;
+    }
+  }
+
+  if (cols == -1) {
+    if (n == 4)
+      YES();
+    else
+      NO();
+    return;
+  }
+
+  // NOTE: didn't check it was square, holy shit throw
+  if (cols == 0 || n % cols != 0 || cols * cols != n) {
+    NO();
+    return;
+  }
+
+  vec<vec<char>> board(n / cols, vec<char>(cols));
+  for (u32 i = 0; i < board.size(); ++i) {
+    for (u32 j = 0; j < board[i].size(); ++j) {
+      board[i][j] = s[i * cols + j];
+    }
+  }
+
+  u32 zeroes = 0;
+  for (auto c : s)
+    if (c == '0')
+      ++zeroes;
+  for (u32 i = 0; i < cols; ++i) {
+    if (s[i] == '0' || s[n - cols + i] == '0') {
+      NO();
+      return;
+    }
+  }
+  for (u32 i = 0; i < n; i += cols) {
+    if (s[i] == '0' || s[i + cols - 1] == '0') {
+      NO();
+      return;
+    }
+  }
+
+  if (n - 2 * cols - 2 * (n / cols) + 4 != zeroes) {
+    NO();
+  } else {
+    YES();
+  }
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+  cin.exceptions(cin.failbit);
+
+  int tc = 1;
+  cin >> tc;
+
+  for (int t = 0; t < tc; ++t) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}

codeforces/970/c.cc

@@ -0,0 +1,91 @@
+#include <bits/stdc++.h>  // {{{
+
+// https://codeforces.com/blog/entry/96344
+
+#pragma GCC optimize("O2,unroll-loops")
+#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
+
+using namespace std;
+
+using i32 = int32_t;
+using u32 = uint32_t;
+using i64 = int64_t;
+using u64 = uint64_t;
+using d64 = double;
+using d128 = long double;
+template <typename T>
+using vec = std::vector<T>;
+template <typename T, size_t N>
+using arr = std::array<T, N>;
+template <typename T1, typename T2>
+using pai = std::pair<T1, T2>;
+
+template <typename T>
+constexpr T MIN = std::numeric_limits<T>::min();
+
+template <typename T>
+constexpr T MAX = std::numeric_limits<T>::max();
+
+template <typename T>
+[[nodiscard]] static T sc(auto&& x) {
+  return static_cast<T>(x);
+}
+
+template <typename T>
+[[nodiscard]] static T sz(auto&& x) {
+  return static_cast<T>(x.size());
+}
+
+static void NO() {
+  std::cout << "NO\n";
+}
+
+static void YES() {
+  std::cout << "YES\n";
+}
+
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+
+#ifdef LOCAL
+#define db(...) std::print(__VA_ARGS__)
+#define dbln(...) std::println(__VA_ARGS__)
+#else
+#define db(...)
+#define dbln(...)
+#endif
+//  }}}
+
+void solve() {
+  i64 l, r;
+  cin >> l >> r;
+
+  i64 lo = 0, hi = r - l + 1;
+
+  while (lo <= hi) {
+    i64 mid = lo + (hi - lo) / 2;
+    if (l + mid * (mid + 1) / 2 <= r) {
+      lo = mid + 1;
+    } else {
+      hi = mid - 1;
+    }
+  }
+
+  // NOTE: hi is # elems ADDING; so also include l implciitly
+  cout << hi + 1 << '\n';
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+  cin.exceptions(cin.failbit);
+
+  int tc = 1;
+  cin >> tc;
+
+  for (int t = 0; t < tc; ++t) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}

codeforces/970/compile_flags.txt

@@ -0,0 +1,31 @@
+-O2
+-Wall
+-Wextra
+-Wpedantic
+-Wshadow
+-Wformat=2
+-Wfloat-equal
+-Wlogical-op
+-Wshift-overflow=2
+-Wnon-virtual-dtor
+-Wold-style-cast
+-Wcast-qual
+-Wuseless-cast
+-Wno-sign-promotion
+-Wcast-align
+-Wunused
+-Woverloaded-virtual
+-Wconversion
+-Wsign-conversion
+-Wmisleading-indentation
+-Wduplicated-cond
+-Wduplicated-branches
+-Wlogical-op
+-Wnull-dereference
+-Wformat=2
+-Wformat-overflow
+-Wformat-truncation
+-Wdouble-promotion
+-Wundef
+-DLOCAL
+-std=c++23

codeforces/970/d.cc

@@ -0,0 +1,163 @@
+#include <bits/stdc++.h>  // {{{
+
+// https://codeforces.com/blog/entry/96344
+
+#pragma GCC optimize("O2,unroll-loops")
+#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
+
+using namespace std;
+
+using i32 = int32_t;
+using u32 = uint32_t;
+using i64 = int64_t;
+using u64 = uint64_t;
+using d64 = double;
+using d128 = long double;
+template <typename T>
+using vec = std::vector<T>;
+template <typename T, size_t N>
+using arr = std::array<T, N>;
+template <typename T1, typename T2>
+using pai = std::pair<T1, T2>;
+
+template <typename T>
+constexpr T MIN = std::numeric_limits<T>::min();
+
+template <typename T>
+constexpr T MAX = std::numeric_limits<T>::max();
+
+template <typename T>
+[[nodiscard]] static T sc(auto&& x) {
+  return static_cast<T>(x);
+}
+
+template <typename T>
+[[nodiscard]] static T sz(auto&& x) {
+  return static_cast<T>(x.size());
+}
+
+static void NO() {
+  std::cout << "NO\n";
+}
+
+static void YES() {
+  std::cout << "YES\n";
+}
+
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+
+#ifdef LOCAL
+#define db(...) std::print(__VA_ARGS__)
+#define dbln(...) std::println(__VA_ARGS__)
+#else
+#define db(...)
+#define dbln(...)
+#endif
+//  }}}
+
+bitset<2 * 100000 + 1> black;
+
+void solve() {
+  black.reset();
+
+  u32 n;
+  cin >> n;
+  vec<u32> a(n);
+  for (auto& e : a) {
+    cin >> e;
+    --e;
+  }
+
+  char c;
+  for (u32 i = 0; i < n; ++i) {
+    cin >> c;
+    if (c == '1')
+      black[i] = true;
+  }
+
+  vec<int> cycle_id(n, -1);
+  vec<int> cycle_pos(n, -1);
+  vec<bool> visited(n, false);
+  vec<int> black_count(n, 0);
+
+  for (u32 start = 0; start < n; ++start) {
+    if (visited[start])
+      continue;
+
+    u32 slow = start;
+    u32 fast = start;
+
+    do {
+      slow = a[slow];
+      fast = a[a[fast]];
+    } while (slow != fast);
+
+    u32 cycle_start = slow;
+    int cycle_length = 1;
+    slow = a[slow];
+
+    while (slow != cycle_start) {
+      cycle_length++;
+      slow = a[slow];
+    }
+
+    slow = cycle_start;
+    int cycle_black = 0;
+    for (int i = 0; i < cycle_length; ++i) {
+      cycle_id[slow] = start;
+      cycle_pos[slow] = i;
+      visited[slow] = true;
+
+      if (black[slow])
+        cycle_black++;
+
+      slow = a[slow];
+    }
+
+    black_count[start] = cycle_black;
+  }
+
+  vec<int> answer(n, 0);
+
+  for (u32 i = 0; i < n; ++i) {
+    if (cycle_id[i] != -1) {
+      answer[i] = black_count[cycle_id[i]];
+    } else {
+      vec<u32> path;
+      u32 curr = i;
+
+      while (cycle_id[curr] == -1) {
+        path.push_back(curr);
+        curr = a[curr];
+      }
+
+      for (u32 node : path) {
+        if (black[node])
+          answer[i]++;
+      }
+
+      answer[i] += black_count[cycle_id[curr]];
+    }
+  }
+
+  for (u32 i = 0; i < n; ++i) {
+    cout << answer[i] << ' ';
+  }
+  cout << '\n';
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+  cin.exceptions(cin.failbit);
+
+  int tc = 1;
+  cin >> tc;
+
+  for (int t = 0; t < tc; ++t) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}

codeforces/970/debug_flags.txt

@@ -0,0 +1,12 @@
+-g3
+-fsanitize=address,undefined
+-fsanitize=float-divide-by-zero
+-fsanitize=float-cast-overflow
+-fno-sanitize-recover=all
+-fstack-protector-all
+-fstack-usage
+-fno-omit-frame-pointer
+-fno-inline
+-ffunction-sections
+-D_GLIBCXX_DEBUG
+-D_GLIBCXX_DEBUG_PEDANTIC

codeforces/970/e.cc

@@ -0,0 +1,122 @@
+#include <bits/stdc++.h>  // {{{
+
+// https://codeforces.com/blog/entry/96344
+
+#pragma GCC optimize("O2,unroll-loops")
+#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
+
+using namespace std;
+
+using i32 = int32_t;
+using u32 = uint32_t;
+using i64 = int64_t;
+using u64 = uint64_t;
+using d64 = double;
+using d128 = long double;
+template <typename T>
+using vec = std::vector<T>;
+template <typename T, size_t N>
+using arr = std::array<T, N>;
+template <typename T1, typename T2>
+using pai = std::pair<T1, T2>;
+
+template <typename T>
+constexpr T MIN = std::numeric_limits<T>::min();
+
+template <typename T>
+constexpr T MAX = std::numeric_limits<T>::max();
+
+template <typename T>
+[[nodiscard]] static T sc(auto&& x) {
+  return static_cast<T>(x);
+}
+
+template <typename T>
+[[nodiscard]] static T sz(auto&& x) {
+  return static_cast<T>(x.size());
+}
+
+static void NO() {
+  std::cout << "NO\n";
+}
+
+static void YES() {
+  std::cout << "YES\n";
+}
+
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+
+#ifdef LOCAL
+#define db(...) std::print(__VA_ARGS__)
+#define dbln(...) std::println(__VA_ARGS__)
+#else
+#define db(...)
+#define dbln(...)
+#endif
+//  }}}
+
+#include <bits/stdc++.h>
+using namespace std;
+
+void solve() {
+  u32 n;
+  cin >> n;
+  string s;
+  cin >> s;
+  int ans = s.size();
+
+  if (n & 1) {
+    vector<int> pref[2] = {vector<int>(26), vector<int>(26)};
+    vector<int> suf[2] = {vector<int>(26), vector<int>(26)};
+
+    for (int i = n - 1; i >= 0; i--) {
+      suf[i % 2][s[i] - 'a']++;
+    }
+
+    for (int i = 0; i < n; i++) {
+      suf[i % 2][s[i] - 'a']--;
+      int odd = n;
+
+      for (int k = 0; k < 2; k++) {
+        int best = 0;
+        for (int j = 0; j < 26; j++) {
+          best = max(best, suf[1 - k][j] + pref[k][j]);
+        }
+        odd -= best;
+      }
+
+      ans = min(ans, odd);
+      pref[i % 2][s[i] - 'a']++;
+    }
+  } else {
+    vector<int> v[2] = {vector<int>(26), vector<int>(26)};
+    for (int i = 0; i < n; i++) {
+      v[i % 2][s[i] - 'a']++;
+    }
+    for (int i = 0; i < 2; i++) {
+      int best = 0;
+      for (int j = 0; j < 26; j++) {
+        best = max(best, v[i][j]);
+      }
+      ans -= best;
+    }
+  }
+
+  cout << ans << '\n';
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+  cin.exceptions(cin.failbit);
+
+  int tc = 1;
+  cin >> tc;
+
+  for (int t = 0; t < tc; ++t) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}

codeforces/970/f.cc

@@ -0,0 +1,58 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+using i64 = long long;
+constexpr i64 MOD = 1e9 + 7;
+
+i64 modinv(i64 a, i64 m) {
+  i64 m0 = m, y = 0, x = 1;
+  if (m == 1)
+    return 0;
+  while (a > 1) {
+    i64 q = a / m;
+    i64 t = m;
+    m = a % m, a = t;
+    t = y;
+    y = x - q * y;
+    x = t;
+  }
+  if (x < 0)
+    x += m0;
+  return x;
+}
+
+void solve() {
+  int n;
+  cin >> n;
+  vector<i64> a(n);
+  for (auto &x : a)
+    cin >> x;
+
+  i64 total_sum = 0, sum_sq = 0;
+  for (auto x : a) {
+    total_sum = (total_sum + x) % MOD;
+    sum_sq = (sum_sq + x * x) % MOD;
+  }
+
+  i64 sum_pairs = (total_sum * total_sum % MOD - sum_sq + MOD) % MOD;
+  sum_pairs = sum_pairs * modinv(2, MOD) % MOD;
+
+  i64 total_pairs = (i64)n * (n - 1) / 2 % MOD;
+  i64 inv_total_pairs = modinv(total_pairs, MOD);
+  i64 ans = sum_pairs * inv_total_pairs % MOD;
+
+  cout << ans << '\n';
+}
+
+int main() {
+  ios::sync_with_stdio(false);
+  cin.tie(nullptr);
+
+  int t;
+  cin >> t;
+  while (t--) {
+    solve();
+  }
+
+  return 0;
+}

codeforces/970/io/a.in

@@ -0,0 +1,6 @@
+5
+0 1
+0 3
+2 0
+2 3
+3 1

codeforces/970/io/a.out

@@ -0,0 +1,8 @@
+NO
+NO
+YES
+YES
+NO
+
+[code]: 0
+[time]: 10.9363 ms

codeforces/970/io/b.in

@@ -0,0 +1,11 @@
+5
+2
+11
+4
+1111
+9
+111101111
+9
+111111111
+12
+111110011111

codeforces/970/io/b.out

@@ -0,0 +1,8 @@
+No
+Yes
+Yes
+No
+No
+
+[code]: 0
+[time]: 4.70805 ms

codeforces/970/io/c.in

@@ -0,0 +1,6 @@
+5
+1 2
+1 5
+2 2
+10 20
+1 1000000000

codeforces/970/io/c.out

@@ -0,0 +1,8 @@
+2
+3
+1
+5
+44721
+
+[code]: 0
+[time]: 3.74532 ms

codeforces/970/io/d.in

@@ -0,0 +1,16 @@
+5
+1
+1
+0
+5
+1 2 4 5 3
+10101
+5
+5 4 1 3 2
+10011
+6
+3 5 6 1 2 4
+010000
+6
+1 2 3 4 5 6
+100110

codeforces/970/io/d.out

@@ -0,0 +1,8 @@
+0 
+1 0 2 2 2 
+3 3 3 3 3 
+0 1 0 0 1 0 
+1 0 0 1 1 0 
+
+[code]: 0
+[time]: 3.73864 ms

codeforces/970/io/e.in

@@ -0,0 +1,21 @@
+10
+1
+a
+2
+ca
+3
+aab
+5
+ababa
+6
+acdada
+9
+ejibmyyju
+6
+bbccbc
+6
+abacba
+5
+bcbca
+5
+dcbdb

codeforces/970/io/e.out

@@ -0,0 +1,13 @@
+1
+0
+1
+1
+2
+6
+2
+3
+1
+1
+
+[code]: 0
+[time]: 4.22215 ms

codeforces/970/io/f.in

@@ -0,0 +1,7 @@
+3
+3
+3 2 3
+4
+2 2 2 4
+5
+1 2 3 4 5

codeforces/970/io/f.out

@@ -0,0 +1,6 @@
+7
+6
+500000012
+
+[code]: 0
+[time]: 4.27008 ms

codeforces/970/makefile

@@ -0,0 +1,28 @@
+.PHONY: run debug clean setup init
+
+SRC = $(word 2,$(MAKECMDGOALS))
+
+.SILENT:
+
+run:
+	sh scripts/run.sh $(SRC)
+
+debug:
+	sh scripts/debug.sh $(SRC)
+
+clean:
+	rm -rf build/*
+
+setup:
+	test -d build || mkdir -p build
+	test -d io || mkdir -p io
+	test -d scripts || mkdir -p scripts
+	test -f compile_flags.txt || cp $(HOME)/.config/cp-template/compile_flags.txt .
+	test -f .clangd || cp $(HOME)/.config/cp-template/.clangd .
+	test -f .clang-format || cp $(HOME)/.config/cp-template/.clang-format .
+
+init:
+	make setup
+
+%:
+	@:

codeforces/970/new

@@ -0,0 +1,66 @@
+void solve() {
+  u32 n;
+  string s;
+  cin >> n >> s;
+
+  // Function to calculate minimum ops for alternating even-length string
+  auto calc_min_ops = [](const vec<u32>& even_count, const vec<u32>& odd_count,
+                         u32 even_positions, u32 odd_positions) -> u32 {
+    // Find most frequent characters in each position type
+    pai<u32, u32> max_even = {0, 0};  // (char, count)
+    pai<u32, u32> second_max_even = {0, 0};
+    pai<u32, u32> max_odd = {0, 0};
+    pai<u32, u32> second_max_odd = {0, 0};
+
+    for (u32 c = 0; c < 26; ++c) {
+      if (even_count[c] > max_even.second) {
+        second_max_even = max_even;
+        max_even = {c, even_count[c]};
+      } else if (even_count[c] > second_max_even.second) {
+        second_max_even = {c, even_count[c]};
+      }
+
+      if (odd_count[c] > max_odd.second) {
+        second_max_odd = max_odd;
+        max_odd = {c, odd_count[c]};
+      } else if (odd_count[c] > second_max_odd.second) {
+        second_max_odd = {c, odd_count[c]};
+      }
+    }
+
+    u32 option1 =
+        (even_positions - max_even.second) + (odd_positions - max_odd.second);
+    u32 option2 = MAX<u32>;
+    if (max_even.first != max_odd.first) {
+      option2 = (even_positions - even_count[max_odd.first]) +
+                (odd_positions - odd_count[max_even.first]);
+    } else {
+      // Try second-best for one position type
+      u32 sub_option1 = (even_positions - second_max_even.second) +
+                        (odd_positions - max_odd.second);
+      u32 sub_option2 = (even_positions - max_even.second) +
+                        (odd_positions - second_max_odd.second);
+      option2 = min(sub_option1, sub_option2);
+    }
+
+    return min(option1, option2);
+  };
+
+  if (n % 2 == 0) {
+    // Even length case
+    vec<u32> even_count(26, 0);
+    vec<u32> odd_count(26, 0);
+
+    for (u32 i = 0; i < n; ++i) {
+      if (i % 2 == 0) {
+        even_count[s[i] - 'a']++;
+      } else {
+        odd_count[s[i] - 'a']++;
+      }
+    }
+
+    cout << calc_min_ops(even_count, odd_count, n / 2, n / 2) << '\n';
+  } else {
+    // O(n) - use suffix?
+  }
+}

codeforces/970/scripts/debug.sh

@@ -0,0 +1,29 @@
+#!/bin/sh
+
+. ./scripts/utils.sh
+
+SRC="$1"
+BASE=$(basename "$SRC" .cc)
+INPUT="${BASE}.in"
+OUTPUT="${BASE}.out"
+DBG_BIN="${BASE}.debug"
+
+test -d build || mkdir -p build
+test -d io || mkdir -p io
+
+test -f "$INPUT" && test ! -f "io/$INPUT" && mv "$INPUT" "io/"
+test -f "$OUTPUT" && test ! -f "io/$OUTPUT" && mv "$OUTPUT" "io/"
+
+test -f "io/$INPUT" || touch "io/$INPUT"
+test -f "io/$OUTPUT" || touch "io/$OUTPUT"
+
+INPUT="io/$INPUT"
+OUTPUT="io/$OUTPUT"
+DBG_BIN="build/$DBG_BIN"
+
+compile_source "$SRC" "$DBG_BIN" "$OUTPUT" @debug_flags.txt
+CODE=$?
+test $CODE -gt 0 && exit $CODE
+
+execute_binary "$DBG_BIN" "$INPUT" "$OUTPUT"
+exit $?

codeforces/970/scripts/run.sh

@@ -0,0 +1,29 @@
+#!/bin/sh
+
+. ./scripts/utils.sh
+
+SRC="$1"
+BASE=$(basename "$SRC" .cc)
+INPUT="${BASE}.in"
+OUTPUT="${BASE}.out"
+RUN_BIN="${BASE}.run"
+
+test -d build || mkdir -p build
+test -d io || mkdir -p io
+
+test -f "$INPUT" && test ! -f "io/$INPUT" && mv "$INPUT" "io/"
+test -f "$OUTPUT" && test ! -f "io/$OUTPUT" && mv "$OUTPUT" "io/"
+
+test -f "io/$INPUT" || touch "io/$INPUT"
+test -f "io/$OUTPUT" || touch "io/$OUTPUT"
+
+INPUT="io/$INPUT"
+OUTPUT="io/$OUTPUT"
+RUN_BIN="build/$RUN_BIN"
+
+compile_source "$SRC" "$RUN_BIN" "$OUTPUT" ""
+CODE=$?
+test $CODE -gt 0 && exit $CODE
+
+execute_binary "$RUN_BIN" "$INPUT" "$OUTPUT"
+exit $?

codeforces/970/scripts/utils.sh

@@ -0,0 +1,53 @@
+#!/bin/sh
+
+execute_binary() {
+  binary="$1"
+  input="$2"
+  output="$3"
+
+  start=$(date '+%s.%N')
+  timeout 2s ./"$binary" <"$input" >"$output" 2>&1
+  CODE=$?
+  end=$(date '+%s.%N')
+  truncate -s "$(head -n 1000 "$output" | wc -c)" "$output"
+
+  if [ $CODE -ge 124 ]; then
+    MSG=''
+    case $CODE in
+    124) MSG='TIMEOUT' ;;
+    128) MSG='SIGILL' ;;
+    130) MSG='SIGABRT' ;;
+    131) MSG='SIGBUS' ;;
+    136) MSG='SIGFPE' ;;
+    135) MSG='SIGSEGV' ;;
+    137) MSG='SIGPIPE' ;;
+    139) MSG='SIGTERM' ;;
+    esac
+    [ $CODE -ne 124 ] && sed -i '$d' "$output"
+    test -n "$MSG" && printf '\n[code]: %s (%s)' "$CODE" "$MSG" >>"$output"
+  else
+    printf '\n[code]: %s' "$CODE" >>"$output"
+  fi
+
+  printf '\n[time]: %s ms' "$(awk "BEGIN {print ($end - $start) * 1000}")" >>$output
+  return $CODE
+}
+
+compile_source() {
+  src="$1"
+  bin="$2"
+  output="$3"
+  flags="$4"
+
+  test -f "$bin" && rm "$bin" || true
+  g++ @compile_flags.txt $flags "$src" -o "$bin" 2>"$output"
+  CODE=$?
+
+  if [ $CODE -gt 0 ]; then
+    printf '\n[code]: %s' "$CODE" >>"$output"
+    return $CODE
+  else
+    echo '' >"$output"
+    return 0
+  fi
+}