[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;

     }

 }