Today is Saturday, I gonna review the tasks I've done this week, and finish today's leetcode's August LeetCoding Challenge with cpp.

LeetCode Review

Valid Sudoku

too easy to review

Maximum Product of Splitted Binary Tree

too easy to review

Decode Ways

too easy to review

Count Good Nodes in Binary Tree

too easy to review

Range Sum Query - Immutable

too easy to review

Implement Queue using Stacks

too easy to review

Min Stack

too easy to review

Count Pairs With XOR in a Range

too easy to review

Check if Binary String Has at Most One Segment of Ones

too easy to review

August LeetCoding Challenge 21

Description

Sudoku Solver

Write a program to solve a Sudoku puzzle by filling the empty cells.

A sudoku solution must satisfy all of the following rules:

1. Each of the digits 1-9 must occur exactly once in each row.
2. Each of the digits 1-9 must occur exactly once in each column.
3. Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid.

The '.' character indicates empty cells.

Example 1:

Input: 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"]]
Output: [["5","3","4","6","7","8","9","1","2"],["6","7","2","1","9","5","3","4","8"],["1","9","8","3","4","2","5","6","7"],["8","5","9","7","6","1","4","2","3"],["4","2","6","8","5","3","7","9","1"],["7","1","3","9","2","4","8","5","6"],["9","6","1","5","3","7","2","8","4"],["2","8","7","4","1","9","6","3","5"],["3","4","5","2","8","6","1","7","9"]]
Explanation: The input board is shown above and the only valid solution is shown below:

Constraints:

• board.length == 9
• board[i].length == 9
• board[i][j] is a digit or '.'.
• It is guaranteed that the input board has only one solution.

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
  vector<int> rows = vector<int>(9);
  vector<int> cols = vector<int>(9);
  vector<int> squares = vector<int>(9);
  void init(vector<vector<char>>& board) {
    for(int i = 0; i < 81; ++i){
      int row = i % 9;
      int col = i / 9;
      int square = i % 9 / 3 * 3 + i / 9 / 3;
      if(board[row][col] == '.') continue;
      rows[row] |= (1 << (board[row][col] - '0'));
      cols[col] |= (1 << (board[row][col] - '0'));
      squares[square] |= (1 << (board[row][col] - '0'));
    }
  }
  bool dfs(vector<vector<char>>& board, int pos) {
    if(pos == 81) return true;
    int row = pos % 9;
    int col = pos / 9;
    int square = pos % 9 / 3 * 3 + pos / 9 / 3;
    if(board[row][col] != '.') return dfs(board, pos+1);
    for(int i = 1; i < 10; ++i) {
      if(rows[row] & (1 << i) ||
        cols[col] & (1 << i) ||
        squares[square] & (1 << i)) continue;
      rows[row] |= (1 << i);
      cols[col] |= (1 << i);
      squares[square] |= (1 << i);
      if(dfs(board, pos+1)) {
        board[row][col] = i+'0';
        return true;
      }
      rows[row] ^= (1 << i);
      cols[col] ^= (1 << i);
      squares[square] ^= (1 << i);
    }
    return false;
  }
public:
  void solveSudoku(vector<vector<char>>& board) {
    init(board);
    dfs(board, 0);
  }
};

// Accepted
// 6/6 cases passed (4 ms)
// Your runtime beats 98.8 % of cpp submissions
// Your memory usage beats 83.27 % of cpp submissions (6.4 MB)