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main.cpp
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class Solution {
public:
void solveSudoku(vector<vector<char>>& board) {
function<bool(int, int, int, int)> check =
[&board](int li, int ri, int lj, int rj) -> bool {
bitset<9> vis;
for (int i = li; i < ri; ++i) {
for (int j = lj; j < rj; ++j) {
if (board[i][j] == '.') continue;
int v = board[i][j] - '0';
if (vis[v]) return false;
vis[v] = true;
}
}
return true;
};
function<bool(int, int)> is_valid = [&board, &check](int i,
int j) -> bool {
if (!check(i, i + 1, 0, 9)) return false;
if (!check(0, 9, j, j + 1)) return false;
int li = i / 3 * 3, ri = li + 3;
int lj = j / 3 * 3, rj = lj + 3;
if (!check(li, ri, lj, rj)) return false;
return true;
};
function<bool(int)> solve = [&board, &is_valid, &solve](int k) -> bool {
if (k == 81) return true;
int i = k / 9, j = k % 9;
if (board[i][j] != '.') return solve(k + 1);
for (char c = '1'; c <= '9'; ++c) {
board[i][j] = c;
if (!is_valid(i, j)) continue;
if (solve(k + 1)) return true;
}
board[i][j] = '.';
return false;
};
solve(0);
}
};