[leetcode]36. Valid Sudoku验证数独

Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

1. Each row must contain the digits 1-9 without repetition.
2. Each column must contain the digits 1-9 without repetition.
3. Each of the 9 3x3 sub-boxes of the grid must contain the digits 1-9 without repetition.

The Sudoku board could be partially filled, where empty cells are filled with the character '.'.

题意：

验证数独

Solution1： HashMap

用int[] map = new int[256] 作为一件简化版的hashmap

扫row、col、box

当前数字c若没在map里出现，则map[c] ++; 若在map里出现过，说明有重复，则返回false。

       

code

public class ValidSudoku {
    public boolean isValidSudoku(char[][] board) {
        // corner case
        if (board == null || board.length != 9 || board[0].length != 9)
            return false;
        //row
        for (int row = 0; row < 9; row++) {
            char[] map = new char[256];
            for (int i = 0; i < 9; i++) {
                char c = board[row][i];
                if (c != '.') {
                    if (map[c] > 0) {
                        return false;
                    } else {
                        map[c]++;
                    }
                }
            }
        }
        // col
        for (int col = 0; col < 9; col++) {
            char[] map = new char[256];
            for (int i = 0; i < 9; i++) {
                char c = board[i][col];
                if (c != '.') {
                    if (map[c] > 0) {
                        return false;
                    } else {
                        map[c]++;
                    }

                }
            }
        }
        //box
        for (int box = 0; box < 9; box++) {
            char[] map = new char[256];
            for (int row = 0; row < 3; row++) {
                for (int col = 0; col < 3; col++) {
                    char c = board[row + 3 * (box / 3)][col + 3 * (box % 3)];
                    if (c != '.') {
                        if (map[c] > 0) {
                            return false;
                        } else {
                            map[c]++;
                        }

                    }

                }

            }

        }
        return true;
    }
}