LeetCode [36] Valid Sudoku

 36. Valid Sudoku

Medium

Determine if a 9 x 9 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 nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.

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.

 

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: true

Example 2:

Input: board = 
[["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.

 

Constraints:

• board.length == 9
• board[i].length == 9
• board[i][j] is a digit or '.'.

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class Solution { public: bool isValidSudoku(vector<vector<char> > &board) { set<char> st; //rows: for(int i=0; i<9; ++i){ st.clear(); for(int j=0; j<9; ++j){ if(board[i][j]!='.'){ if(st.find(board[i][j])!=st.end()) return false; else st.insert(board[i][j]); } } } //columns: for(int i=0; i<9; ++i){ st.clear(); for(int j=0; j<9; ++j){ if(board[j][i]!='.'){ if(st.find(board[j][i])!=st.end()) return false; else st.insert(board[j][i]); } } } //blocks: for(int i=0; i<3; ++i){ for(int j=0; j<3; ++j){ st.clear(); for(int k=0; k<9; ++k){ int r = i*3+k/3; int c = j*3+k%3; if(board[r][c]!='.'){ if(st.find(board[r][c])!=st.end()) return false; else st.insert(board[r][c]); } } } } return true; } };

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class Solution { public boolean isValidSudoku(char[][] board) { //rows: for(int i=0; i<9; ++i){ int[] nums = new int[9]; for(int j=0; j<9; ++j){ if(board[i][j]=='.') continue; int d = board[i][j]-'1'; if(!(d>=0 && d<9) || nums[d]>0){ // System.out.println(i+"+"+j); return false; } nums[d]=1; } } //cols: for(int j=0; j<9; ++j){ int[] nums = new int[9]; for(int i=0; i<9; ++i){ if(board[i][j]=='.') continue; int d = board[i][j]-'1'; if(nums[d]>0){ // System.out.println(i+"-"+j); return false; } nums[d]=1; } } //blks: for(int k=0; k<9; ++k){ int[] nums = new int[9]; for(int b=0; b<9; ++b){ int i = k/3*3+b/3; int j = k%3*3+b%3; if(board[i][j]=='.') continue; int d = board[i][j]-'1'; if(nums[d]>0){ // System.out.println(k+"*"+b+"*"+i+"*"+j); return false; } nums[d]=1; } } return true; } }