00036-valid_sudoku.java

// 36: Valid Sudoku
// https://leetcode.com/problems/valid-sudoku/


class Solution {
    // SOLUTION
    public boolean isValidSudoku(char[][] board) {
        int used1[][] = new int[9][9], used2[][] = new int[9][9], used3[][] = new int[9][9];
        
        for (int i=0; i<board.length; ++i)
            for (int j=0; j<board[i].length; ++j)
                if (board[i][j]!='.') {
                    int num = board[i][j]-'0' - 1;
                    int k = i/3 * 3 + j/3;
                    
                    if (used1[i][num]!=0 || used2[j][num]!=0 || used3[k][num]!=0)
                        return false;
                    
                    used1[i][num] = used2[j][num] = used3[k][num] = 1;
                }

        return true;
    }

    public static void main(String[] args) {
        Solution o = new Solution();

        // INPUT
        char[][] board = 
        {
            {'5','3','.','.','7','.','.','.','.'},
            {'6','.','.','1','9','5','.','.','.'},
            {'.','9','8','.','.','.','.','6','.'},
            {'8','.','.','.','6','.','.','.','3'},
            {'4','.','.','8','.','3','.','.','1'},
            {'7','.','.','.','2','.','.','.','6'},
            {'.','6','.','.','.','.','2','8','.'},
            {'.','.','.','4','1','9','.','.','5'},
            {'.','.','.','.','8','.','.','7','9'}
        };

        // OUTPUT
        var result = o.isValidSudoku(board);
        System.out.println((result ? "true" : "false"));
    }
}