Create 21_sudokuSolver.cpp

Author: FazeelUsmani

08 August Leetcode Challenge 2021/21_sudokuSolver.cpp

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+class Solution {
+public:
+ vector<pair<int, int>> emptyCells;
+ int rows[9] = {}, cols[9] = {}, boxes[9] = {};
+ void solveSudoku(vector<vector<char>>& board) {
+ for (int r = 0; r < 9; r++) {
+ for (int c = 0; c < 9; c++) {
+ if (board[r][c] == '.') {
+ emptyCells.emplace_back(r, c);
+ } else {
+ int val = board[r][c] - '0';
+ int boxPos = (r / 3) * 3 + (c / 3);
+ rows[r] |= 1 << val;
+ cols[c] |= 1 << val;
+ boxes[boxPos] |= 1 << val;
+ }
+ }
+ }
+ backtracking(board, 0);
+ }
+ bool backtracking(vector<vector<char>>& board, int i) {
+ if (i == emptyCells.size()) return true; // Check if we filled all empty cells?
+
+ int r = emptyCells[i].first, c = emptyCells[i].second, boxPos = (r / 3) * 3 + c / 3;
+ for (int val = 1; val <= 9; ++val) {
+ if (getBit(rows[r], val) || getBit(cols[c], val) || getBit(boxes[boxPos], val)) continue; // skip if that value is existed!
+ board[r][c] = ('0' + val);
+ int oldRow = rows[r], oldCol = cols[c], oldBox = boxes[boxPos]; // backup old values
+ rows[r] |= 1 << val;
+ cols[c] |= 1 << val;
+ boxes[boxPos] |= 1 << val;
+ if (backtracking(board, i + 1)) return true;
+ rows[r] = oldRow; // backtrack
+ cols[c] = oldCol; // backtrack
+ boxes[boxPos] = oldBox; // backtrack
+ }
+ return false;
+ }
+ int getBit(int x, int k) {
+ return (x >> k) & 1;
+ }
+};