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Diffstat (limited to 'solve_bt.cpp')
| -rw-r--r-- | solve_bt.cpp | 248 |
1 files changed, 248 insertions, 0 deletions
diff --git a/solve_bt.cpp b/solve_bt.cpp new file mode 100644 index 0000000..418e286 --- /dev/null +++ b/solve_bt.cpp @@ -0,0 +1,248 @@ +#include <iostream> +#include <iomanip> +#include <string> +#include <vector> +#include <cstring> +#include <cstdint> +#include <cassert> + +using namespace std; + + +struct Sudoku { + int8_t bd[81]; + uint16_t poss[81]; + int nfull = 0; + + Sudoku() { + for (int i = 0; i < 81; i++) { + poss[i] = 0x1ff; + } + } + + inline int8_t& operator[](int8_t i) {return bd[i];} + inline const int8_t& operator[](int8_t i) const {return bd[i];} +}; + +static istream& operator>>(istream &in, Sudoku &su) { + su.nfull = 0; + + for (int i = 0; i < 81; i++) { + char c; + in >> c; + if (c == '.') { + su[i] = -1; + } else { + assert('1' <= c && c <= '9'); + su[i] = c - '1'; + su.nfull++; + } + } + + return in; +} + +static ostream& operator<<(ostream &os, const Sudoku &su) { + for (int y = 0; y < 9; y++) { + if (y != 0) { + os << endl; + if (y % 3 == 0) os << endl; + } + + for (int x = 0; x < 9; x++) { + if (x != 0) { + os << ' '; + if (x % 3 == 0) os << ' '; + } + int8_t v = su[9 * y + x]; + if (v == -1) os << '.'; + else os << (int)v + 1; + // string s; + // for (int i = 0; i < 9; i++) { + // if (su.poss[9 * y + x] & (1<<i)) s += '1' + i; + // } + // os << '(' << setw(9) << s << ')'; + } + } + + return os; +} + +static bool isValid(const Sudoku &su) { + for (int y = 0; y < 9; y++) { + int i = 9 * y; + uint8_t seen[9]; + memset(seen, 0, 9); + for (int x = 0; x < 9; x++, i++) { + int v = su[i]; + if (v != -1) { + if (seen[v]) return false; + else seen[v] = 1; + } + } + } + + for (int x = 0; x < 9; x++) { + int i = x; + uint8_t seen[9]; + memset(seen, 0, 9); + for (int y = 0; y < 9; y++, i += 9) { + int v = su[i]; + if (v != -1) { + if (seen[v]) return false; + else seen[v] = 1; + } + } + } + + int i = 0; + for (int by = 0; by < 9; by += 3) { + for (int bx = 0; bx < 9; bx += 3) { + uint8_t seen[9]; + memset(seen, 0, 9); + + int j = i; + for (int y = 0; y < 3; y++) { + for (int x = 0; x < 3; x++) { + int v = su[j]; + if (v != -1) { + if (seen[v]) return false; + else seen[v] = 1; + } + j++; + } + j += 6; + } + + i += 3; + } + i += 18; + } + + return true; +} + +vector<Sudoku> solutions; + +static void scratchAround(Sudoku &su, int idx, int x, int y) { + uint16_t mask = 0x1ff & ~(1 << su[idx]); + + for (int i = 0; i < 9; i++) { + su.poss[9 * y + i] &= mask; + su.poss[9 * i + x] &= mask; + } + + int bx = x / 3 * 3, by = y / 3 * 3; + for (int yi = 0; yi < 3; yi++) { + for (int xi = 0; xi < 3; xi++) { + su.poss[9 * (by + yi) + bx + xi] &= mask; + } + } +} + +static void scratchAround(Sudoku &su, int idx) { + scratchAround(su, idx, idx % 9, idx / 9); +} + +static void scratchAround(Sudoku &su, int x, int y) { + scratchAround(su, 9 * y + x, x, y); +} + +static void solveDestructive(Sudoku &su) { + // cerr << "solveDestructive(" << su.nfull << ")" << endl; + + for (int y = 0, i = 0; y < 9; y++) { + for (int x = 0; x < 9; x++, i++) { + if (su[i] != -1) continue; + + if (__builtin_popcount(su.poss[i]) == 1) { + su[i] = __builtin_ctz(su.poss[i]); + su.nfull++; + scratchAround(su, i); + } + } + } + + if (su.nfull == 81) { + if (isValid(su)) { + solutions.push_back(su); + } + return; + } + + int mincount = 99, minat = -1; + + for (int y = 0, i = 0; y < 9; y++) { + for (int x = 0; x < 9; x++, i++) { + if (su[i] != -1) continue; + + int count = __builtin_popcount((uint32_t)su.poss[i]); + if (count < mincount) { + mincount = count; + minat = i; + } + } + } + + if (mincount == 1) { + // do a tail call + solveDestructive(su); + return; + } + + if (mincount == 0) { + // invalid + return; + } + + // cerr << "minat = " << minat << " "; + // cerr << "mincount = " << mincount << endl; + + int i = minat; + for (int v = 0; v < 9; v++) { + if ((su.poss[i] & (1 << v)) == 0) continue; + + Sudoku su2 = su; + su2[i] = v; + su2.nfull++; + // cerr << "try " << v << endl; + if (!isValid(su2)) { + // cerr << " invalid" << endl; + continue; + } + + scratchAround(su2, i); + solveDestructive(su2); + } +} + +static void solve(const Sudoku &su) { + Sudoku su2 = su; + solveDestructive(su2); +} + + +static void cleanPoss(Sudoku &su) { + for (int y = 0; y < 9; y++) { + for (int x = 0; x < 9; x++) { + scratchAround(su, x, y); + } + } +} + +int main() { + Sudoku su; + cin >> su; + + solutions.clear(); + cleanPoss(su); + solve(su); + + if (solutions.size() != 1) { + cout << solutions.size() << " solutions found:" << endl; + } + + for (const Sudoku &su2 : solutions) { + cout << su2 << endl << endl; + } +} |