java 37. Sudoku Solver（＃）。java

Posted 2021-05-08

public class Solution {
    private int[][] col = new int[9][9];
    private int[][] row = new int[9][9];
    private int[][] grid = new int[9][9];
    public void solveSudoku(char[][] board) {
        for(int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++){
                if (board[i][j] != '.') {
                    int num = board[i][j] - '1';
                    row[i][num] = col[j][num] = grid[i/3*3+j/3][num] = 1;
                    // i/3 would be int divide
                    // 9 grid
                }
            }
        }
        dfs(board, 0);
    }
    
    private boolean dfs(char[][] board, int pos) {
        if (pos == 81) {
            return true;
        }
        int x = pos/9, y = pos%9;
        if (board[x][y] != '.') {
            return dfs(board, pos + 1);
        }
        for (int i = 0; i < 9; i++) {
            if (row[x][i]  == 0 && col[y][i] == 0 && grid[x/3*3+y/3][i] == 0){
                row[x][i] = col[y][i] = grid[x/3*3+y/3][i] = 1;
                if (dfs(board, pos+1)) {
                    board[x][y] = (char)(i + '1');
                    return true;
                }
                row[x][i] = 0;
                col[y][i] = 0;
                grid[x/3*3+y/3][i] = 0;
            }
        }
        return false;
    }
    
}

public class Solution {
    private boolean solver(int idx, char[][] board, ArrayList<Integer> stack, int[] store) {
        if (idx == stack.size()) return true;
        int n = stack.get(idx);
        int y = n / 9;
        int x = n - y * 9;
        int h = y;
        int v = 9 + x;
        int b = 18 + (y / 3 * 3 + x / 3);
        int available = ~store[h] & ~store[v] & ~store[b] & 0b111111111;
        while (available > 0) {
            int bit = available & -available;
            int num = Integer.numberOfTrailingZeros(bit);
            store[h] ^= bit;
            store[v] ^= bit;
            store[b] ^= bit;
            board[y][x] = (char)(num + '1');
            if (solver(idx + 1, board, stack, store)) return true;
            store[h] ^= bit;
            store[v] ^= bit;
            store[b] ^= bit;
            // board[y][x] = '.';
            available &= available - 1;
        }
        return false;
    }
    public void solveSudoku(char[][] board) {
        ArrayList<Integer> stack =  new ArrayList<>();
        // int[] stack = new int[81];
        int len = 0;
        int[] store = new int[27]; // 0-8 h, 9 - 17 v, 18 - 26 b
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                if (board[i][j] == '.') stack.add(i * 9 + j);
                else {
                    int h = i;
                    int v = 9 + j;
                    int b = 18 + (i / 3 * 3 + j / 3);
                    store[h] ^= 1 << board[i][j] - '1';
                    store[v] ^= 1 << board[i][j] - '1';
                    store[b] ^= 1 << board[i][j] - '1';
                }
            }
        }
        solver(0, board, stack, store);
    }
}

public class Solution {
    public void solveSudoku(char[][] board) {
        if(board == null || board.length == 0)
            return;
        solve(board);
    }
    
    public boolean solve(char[][] board){
        for(int i = 0; i < board.length; i++){
            for(int j = 0; j < board[0].length; j++){
                if(board[i][j] == '.'){
                    for(char c = '1'; c <= '9'; c++){//trial. Try 1 through 9
                        if(isValid(board, i, j, c)){
                            board[i][j] = c; //Put c for this cell
                            
                            if(solve(board))
                                return true; //If it's the solution return true
                            else
                                board[i][j] = '.'; //Otherwise go back
                        }
                    }
                    
                    return false;
                }
            }
        }
        return true;
    }
    
    private boolean isValid(char[][] board, int row, int col, char c){
        for(int i = 0; i < 9; i++) {
            if(board[i][col] != '.' && board[i][col] == c) return false; //check row
            if(board[row][i] != '.' && board[row][i] == c) return false; //check column
            if(board[3 * (row / 3) + i / 3][ 3 * (col / 3) + i % 3] != '.' && 
board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == c) return false; //check 3*3 block
        }
        return true;
    }
}