Initial Commit

sudokuSolver.cpp

+#include <iostream>
+#include <map>
+#include <set>
+//Backtracking & recursive algorithm to solve sudoku puzzle if possible, to be implemented in python with a GUI later.
+
+
+//Sudoku rules: The grid has 81 squares: 9 boxes of 9 squares. Each box must contain
+//all numbers 1-9 in its squares, and each number can appear only once in any row, 
+//column, or box.
+bool solveSudoku(int **grid){
+    std::pair<int,int> zeroIndex; //row,col of the zero to be filled.
+    bool foundZero = findZero(grid, zeroIndex);
+    if(foundZero){
+        for(int i = 1; i < 10; ++i){
+            grid[zeroIndex.first,zeroIndex.second] = i;
+            if(checkSolution(grid, zeroIndex.first, zeroIndex.second)){
+                solveSudoku(grid);
+            }
+        }
+        grid[zeroIndex.first,zeroIndex.second] = 0; 
+        return false;
+    } else {
+        return true; //solved
+    }
+}
+
+//Helper functions:
+//checks the solution for a given index and returns true if valid.
+bool checkSolution(int **grid, const int &row, const int &col){ 
+    for(int i = 0; i < 9; ++i){
+        if(grid[i][col] == grid[row][col] && i != row) {
+            return false;
+        } else if (grid[row][i] == grid[row][col] && i != col){
+            return false;
+        }
+    }
+    return true;
+}
+
+//Finds the index of the next zero to be solved.
+bool findZero(int **grid, std::pair<int,int> &zeroIndex){
+    for(int i = 0; i < 9; ++i){
+        for(int j = 0; j < 9; ++j){
+            if(grid[i][j] == 0) {
+                zeroIndex.first = i;
+                zeroIndex.second = j;
+                return true;
+            }
+        }
+    }
+    return false;
+
+}
+
+//Prints the board.
+void printBoard(){
+    for(int i = 0; i < 9; ++i){
+        for(int j = 0; j < 9; ++j){
+            std::cout << grid{i][j] << " ";}
+        }
+        std::cout << std::endl;
+    }
+}
+
+int main() {
+    //Easy Grid:
+    int grid[9][9] = { { 1, 2, 3, 0, 5, 6 ,7 ,8, 9 },
+	{0, 5, 6, 7, 8, 9, 1, 2, 3},
+	{7, 8, 0, 1, 2, 3, 4, 5, 6},
+	{2, 1, 4, 3, 6, 5, 0, 9 ,7},
+	{3, 0, 5, 8, 9, 7, 2, 1,4},
+	{8, 9, 7, 2, 1, 4, 3, 6, 0},
+	{5, 3, 1, 6, 4, 2, 9, 0, 8},
+	{6 ,4 ,2, 9, 0, 8, 5, 3, 1},
+	{9, 7, 8, 0, 3, 1, 6, 4, 2} };
+
+    //Medium Grid:
+
+    //Hard Grid:
+
+    if(solveSudoku(grid)==true) {std::cout << "Solved!" << std::endl;}
+    else {std::cout << "Unsolvable :(" << std::endl;}
+
+    printBoard();
+
+    return 0;
+}
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