98 lines
1.9 KiB
C++
98 lines
1.9 KiB
C++
#include <bits/stdc++.h> // {{{
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// https://codeforces.com/blog/entry/96344
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#pragma GCC optimize("O2,unroll-loops")
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#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
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using namespace std;
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template <typename T>
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constexpr T MIN = std::numeric_limits<T>::min();
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template <typename T>
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constexpr T MAX = std::numeric_limits<T>::max();
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template <typename T>
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[[nodiscard]] static T sc(auto &&x) {
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return static_cast<T>(x);
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}
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template <typename T>
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[[nodiscard]] static T sz(auto &&x) {
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return static_cast<T>(x.size());
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}
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using ll = long long;
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using ld = long double;
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template <typename T>
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using vec = std::vector<T>;
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template <typename T, size_t N>
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using arr = std::array<T, N>;
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#define ff first
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#define ss second
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#define eb emplace_back
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#define pb push_back
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#define all(x) (x).begin(), (x).end()
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#define rall(x) (x).rbegin(), (x).rend()
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// }}}
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constexpr static int N = 8;
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vec<string> board(N);
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// SC: O(n) for recursive space + queens
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// TC: O(n*n*n) - every row every col check all queens
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// NOTE: pruning
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ll backtrack(vec<int> &queens) {
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if (queens.size() == N) {
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return 1;
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}
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ll r = queens.size();
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ll ans = 0;
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for (int C = 0; C < N; ++C) {
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if (board[r][C] == '*')
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continue;
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bool bad = false;
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for (int qr = 0; qr < sz<int>(queens); ++qr) {
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int qc = queens[qr];
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// Q: does it fall on the DIAGONAL?
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// for each line, is there an integer sol'n?
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// y - qr = x - qc -> x - qc + qr <- n queens
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// or y - qr = -x + qc -> y = -x + qc + qr
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if (qc == C || abs(r - qr) == abs(C - qc)) {
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bad = true;
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break;
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}
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}
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if (bad)
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continue;
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queens.eb(C);
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ans += backtrack(queens);
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queens.pop_back();
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}
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return ans;
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}
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void solve() {
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for (int i = 0; i < N; ++i) {
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cin >> board[i];
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}
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vec<int> queens;
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ll ans = backtrack(queens);
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cout << ans << endl;
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}
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int main() { // {{{
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cin.tie(nullptr)->sync_with_stdio(false);
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solve();
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return 0;
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}
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// }}}
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