leetcode-solutions/src/leetcode/ValidSudoku.java at master · eko1995/leetcode-solutions · GitHub

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package leetcode;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * @author eko
 * @date 2018/10/22 9:54 AM
 *
 * Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
 *
 * Each row must contain the digits 1-9 without repetition.
 * Each column must contain the digits 1-9 without repetition.
 * Each of the 9 3x3 sub-boxes of the grid must contain the digits 1-9 without repetition.
 *
 * A partially filled sudoku which is valid.
 *
 * The Sudoku board could be partially filled, where empty cells are filled with the character '.'.
 *
 * Example 1:
 *
 * Input:
 * [
 *   ["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: true
 * Example 2:
 *
 * Input:
 * [
 *   ["8","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: false
 * Explanation: Same as Example 1, except with the 5 in the top left corner being
 *     modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.
 * Note:
 *
 * A Sudoku board (partially filled) could be valid but is not necessarily solvable.
 * Only the filled cells need to be validated according to the mentioned rules.
 * The given board contain only digits 1-9 and the character '.'.
 * The given board size is always 9x9.
 *
 */
public class ValidSudoku {
    public static void main(String[] args) {
        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'}
        };
        boolean res = new ValidSudoku().isValidSudoku(board);
        System.out.println(res);
    }

    public boolean isValidSudoku(char[][] board) {
        List<Set<Character>> colList = new ArrayList<>();
        List<Set<Character>> subBoxList = new ArrayList<>();
        for (int i = 0; i < 9; i++) {
            colList.add(new HashSet<>());
            subBoxList.add(new HashSet<>());
        }
        for (int i = 0; i < board.length; i++) {
            Set<Character> row = new HashSet<>();
            for (int j = 0; j < board.length; j++) {
                if (board[i][j] != '.') {
                    if (row.contains(board[i][j])) {
                        return false;
                    } else {
                        row.add(board[i][j]);
                    }
                    if (colList.get(j).contains(board[i][j])) {
                        return false;
                    } else {
                        colList.get(j).add(board[i][j]);
                    }
                    int index = (i / 3) * 3 + j / 3;
                    if (subBoxList.get(index).contains(board[i][j])) {
                        return false;
                    } else {
                        subBoxList.get(index).add(board[i][j]);
                    }
                }
            }
        }
        return true;
    }
}


/**
 *  Better solution from others:
 *
 *  public boolean isValidSudoku(char[][] board) {
 *
 *         for(int i = 0; i < 9; i++) {
 *             boolean[] check = new boolean[10];
 *             for(int j = 0; j < 9; j++) {
 *                 if (board[i][j] == '.') continue;
 *                 int num = board[i][j] - '0';
 *                 if (check[num]) return false;
 *                 else check[num] = true;
 *             }
 *         }
 *
 *         for(int i = 0; i < 9; i++) {
 *             boolean[] check = new boolean[10];
 *             for(int j = 0; j < 9; j++) {
 *                 if (board[j][i] == '.') continue;
 *                 int num = board[j][i] - '0';
 *                 if (check[num]) return false;
 *                 else check[num] = true;
 *             }
 *         }
 *
 *
 *         for (int ii = 0; ii < 9; ii += 3) {
 *             for (int jj = 0; jj < 9; jj += 3) {
 *
 *                 boolean[] check = new boolean[10];
 *                 for(int i = ii; i < ii+3; i++) {
 *                     for(int j = jj; j < jj+3; j++) {
 *                         if (board[i][j] == '.') continue;
 *                         int num = board[i][j] - '0';
 *                         if (check[num]) return false;
 *                         else check[num] = true;
 *                     }
 *                 }
 *             }
 *         }
 *
 *         return true;
 *     }
 */