Valid Sudoku

描述

Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules http://sudoku.com.au/TheRules.aspx .

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

Valid Sudoku

Figure: Valid Sudoku

分析

细节实现题。

代码

  1. // Valid Sudoku
  2. // 时间复杂度O(n^2)，空间复杂度O(1)
  3. public class Solution {
  4.     public boolean isValidSudoku(char[][] board) {
  5.         boolean[] used = new boolean[9];
  7.         for (int i = 0; i < 9; ++i) {
  8.             Arrays.fill(used, false);
  10.             for (int j = 0; j < 9; ++j) // 检查行
  11.                 if (!check(board[i][j], used))
  12.                     return false;
  14.             Arrays.fill(used, false);
  16.             for (int j = 0; j < 9; ++j) // 检查列
  17.                 if (!check(board[j][i], used))
  18.                     return false;
  19.         }
  21.         for (int r = 0; r < 3; ++r) // 检查 9 个子格子
  22.             for (int c = 0; c < 3; ++c) {
  23.                 Arrays.fill(used, false);
  25.                 for (int i = r * 3; i < r * 3 + 3; ++i)
  26.                     for (int j = c * 3; j < c * 3 + 3; ++j)
  27.                         if (!check(board[i][j], used))
  28.                             return false;
  29.             }
  31.         return true;
  32.     }
  34.     private static boolean check(char ch, boolean[] used) {
  35.         if (ch == '.') return true;
  37.         if (used[ch - '1']) return false;
  39.         return used[ch - '1'] = true;
  40.     }
  41. };

相关题目

原文: https://soulmachine.gitbooks.io/algorithm-essentials/content/java/linear-list/array/valid-sudoku.html