README.md

36. Valid Sudoku

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.

A partially filled sudoku which is valid.

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

Example 1:

Input:
[
  ["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: true

Example 2:

Input:
[
  ["8","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: false
Explanation: Same as Example 1, except with the 5 in the top left corner being modified to 8.
Since there are two 8's in the top left 3x3 sub-box, it is invalid.

Note:

• A Sudoku board (partially filled) could be valid but is not necessarily solvable.
• Only the filled cells need to be validated according to the mentioned rules.
• The given board contain only digits 1-9 and the character '.'.
• The given board size is always 9x9.

Solutions (Rust)

1. Solution1

use std::collections::HashSet;

impl Solution {
    pub fn is_valid_sudoku(board: Vec<Vec<char>>) -> bool {
        let mut cnt_row;
        let mut set_row = HashSet::new();
        let mut cnt_col = vec![0; 9];
        let mut set_col = vec![HashSet::new(); 9];
        let mut cnt_sub = vec![0; 3];
        let mut set_sub = vec![HashSet::new(); 3];

        for row in 0..9 {
            cnt_row = 0;
            set_row.clear();
            if row % 3 == 0 {
                for i in 0..3 {
                    cnt_sub[i] = 0;
                    set_sub[i].clear();
                }
            }

            for col in 0..9 {
                if board[row][col] != '.' {
                    cnt_row += 1;
                    set_row.insert(board[row][col]);
                    cnt_col[col] += 1;
                    set_col[col].insert(board[row][col]);
                    cnt_sub[col / 3] += 1;
                    set_sub[col / 3].insert(board[row][col]);
                }

                if col % 3 == 2 {
                    if cnt_sub[col / 3] != set_sub[col / 3].len() {
                        return false;
                    }
                }
                if row == 8 {
                    if cnt_col[col] != set_col[col].len() {
                        return false;
                    }
                }
            }
            if cnt_row != set_row.len() {
                return false;
            }
        }
        true
    }
}

2. Solution2

impl Solution {
    pub fn is_valid_sudoku(board: Vec<Vec<char>>) -> bool {
        let mut ans = vec![vec![vec![false; 9]; 3] ;9];
        for row in 0..9 {
            for col in 0..9 {
                let sub = row / 3 * 3 + col / 3;
                if board[row][col] != '.' {
                    let n = board[row][col].to_digit(10).unwrap() as usize - 1;
                    if ans[n][0][row] || ans[n][1][col] || ans[n][2][sub] {
                        return false;
                    }
                    ans[n][0][row] = true;
                    ans[n][1][col] = true;
                    ans[n][2][sub] = true;
                }
            }
        }
        true
    }
}