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. class Solution {
  4. public:
  5.     bool isValidSudoku(const vector<vector<char>>& board) {
  6.         bool used[9];
  8.         for (int i = 0; i < 9; ++i) {
  9.             fill(used, used + 9, false);
  11.             for (int j = 0; j < 9; ++j) // 检查行
  12.                 if (!check(board[i][j], used))
  13.                     return false;
  15.             fill(used, used + 9, false);
  17.             for (int j = 0; j < 9; ++j) // 检查列
  18.                 if (!check(board[j][i], used))
  19.                     return false;
  20.         }
  22.         for (int r = 0; r < 3; ++r) // 检查 9 个子格子
  23.             for (int c = 0; c < 3; ++c) {
  24.                 fill(used, used + 9, false);
  26.                 for (int i = r * 3; i < r * 3 + 3; ++i)
  27.                     for (int j = c * 3; j < c * 3 + 3; ++j)
  28.                         if (!check(board[i][j], used))
  29.                             return false;
  30.             }
  32.         return true;
  33.     }
  35.     bool check(char ch, bool used[9]) {
  36.         if (ch == '.') return true;
  38.         if (used[ch - '1']) return false;
  40.         return used[ch - '1'] = true;
  41.     }
  42. };

相关题目

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