Updating C++ solution for 36.Valid Sudoku

Updated the code, using boolean matrices to account for seen values in rows, cols, and sub boxes. More readable code.

cpp/neetcode_150/01_arrays_&_hashing/valid_sudoku.cpp

@@ -1,66 +1,38 @@
 /*
  Determine if a 9x9 Sudoku board is valid (no repeats)
 
- Hash set to store seen values, check rows, cols, blocks
+ Boolean matrices to store seen values. Check rows, cols, 3x3 sub-boxes
 
- Time: O(n^2)
- Space: O(n^2)
+ Time: O(cnt^2)
+ Space: O(cnt^2)
 */
 
 class Solution {
 public:
  bool isValidSudoku(vector<vector<char>>& board) {
- unordered_set<char> s;
+ const int cnt = 9;
+ bool row[cnt][cnt] = {false};
+ bool col[cnt][cnt] = {false};
+ bool sub[cnt][cnt] = {false};
 
- for (int i = 0; i < 9; i++) {
- for (int j = 0; j < 9; j++) {
- if (board[i][j] == '.') {
- continue;
- }
- auto it = s.find(board[i][j]);
- if (it != s.end()) {
- return false;
- } else {
- s.insert(board[i][j]);
- }
- }
- s.clear();
- }
-
- for (int i = 0; i < 9; i++) {
- for (int j = 0; j < 9; j++) {
- if (board[j][i] == '.') {
- continue;
- }
- auto it = s.find(board[j][i]);
- if (it != s.end()) {
+ for(int r = 0; r < cnt; ++r){
+ for(int c = 0; c < cnt; ++c){
+ if(board[r][c] == '.')
+ continue; // if not number pass
+
+ int idx = board[r][c] - '0' - 1; //char to num idx
+ int area = (r/3) * 3 + (c/3);
+
+ //if number already exists
+ if(row[r][idx] || col[c][idx] || sub[area][idx]){
  return false;
- } else {
- s.insert(board[j][i]);
- }
- }
- s.clear();
- }
-
- for (int iCount = 0; iCount < 9; iCount += 3) {
- for (int jCount = 0; jCount < 9; jCount += 3) {
- for (int i = iCount; i < iCount + 3; i++) {
- for (int j = jCount; j < jCount + 3; j++) {
- if (board[i][j] == '.') {
- continue;
- }
- auto it = s.find(board[i][j]);
- if (it != s.end()) {
- return false;
- } else {
- s.insert(board[i][j]);
- }
- }
  }
- s.clear();
+
+ row[r][idx] = true;
+ col[c][idx] = true;
+ sub[area][idx] = true;
  }
  }
-
  return true;
  }
 };