Merge pull request #115 from ashish1500616/SudokuAlgorithmBacktracking

#7 Backtracking Algorithm's Add Sudoku Algorithm In Cpp.

Author: matthewsamuel95

BackTracking/SudokuAlgorithm/SudokuAlgorithm.cpp

@@ -0,0 +1,100 @@
+#include <stdio.h>
+
+#define UNASSIGNED 0
+
+#define N 9
+
+bool FindUnassignedLocation(int grid[N][N], int& row, int& col);
+
+bool isSafe(int grid[N][N], int row, int col, int num);
+
+bool SolveSudoku(int grid[N][N])
+{
+    int row, col;
+
+    if (!FindUnassignedLocation(grid, row, col))
+        return true;
+
+    for (int num = 1; num <= 9; num++) {
+
+        if (isSafe(grid, row, col, num)) {
+
+            grid[row][col] = num;
+
+            if (SolveSudoku(grid))
+                return true;
+
+            grid[row][col] = UNASSIGNED;
+        }
+    }
+    return false;
+}
+
+bool FindUnassignedLocation(int grid[N][N], int& row, int& col)
+{
+    for (row = 0; row < N; row++)
+        for (col = 0; col < N; col++)
+            if (grid[row][col] == UNASSIGNED)
+                return true;
+    return false;
+}
+
+bool UsedInRow(int grid[N][N], int row, int num)
+{
+    for (int col = 0; col < N; col++)
+        if (grid[row][col] == num)
+            return true;
+    return false;
+}
+
+bool UsedInCol(int grid[N][N], int col, int num)
+{
+    for (int row = 0; row < N; row++)
+        if (grid[row][col] == num)
+            return true;
+    return false;
+}
+
+bool UsedInBox(int grid[N][N], int boxStartRow, int boxStartCol, int num)
+{
+    for (int row = 0; row < 3; row++)
+        for (int col = 0; col < 3; col++)
+            if (grid[row + boxStartRow][col + boxStartCol] == num)
+                return true;
+    return false;
+}
+
+bool isSafe(int grid[N][N], int row, int col, int num)
+{
+
+    return !UsedInRow(grid, row, num) && !UsedInCol(grid, col, num) && !UsedInBox(grid, row - row % 3, col - col % 3, num);
+}
+
+void printGrid(int grid[N][N])
+{
+    for (int row = 0; row < N; row++) {
+        for (int col = 0; col < N; col++)
+            printf("%2d", grid[row][col]);
+        printf("\n");
+    }
+}
+
+int main()
+{
+
+    int grid[N][N] = { { 3, 0, 6, 5, 0, 8, 4, 0, 0 },
+        { 5, 2, 0, 0, 0, 0, 0, 0, 0 },
+        { 0, 8, 7, 0, 0, 0, 0, 3, 1 },
+        { 0, 0, 3, 0, 1, 0, 0, 8, 0 },
+        { 9, 0, 0, 8, 6, 3, 0, 0, 5 },
+        { 0, 5, 0, 0, 9, 0, 6, 0, 0 },
+        { 1, 3, 0, 0, 0, 0, 2, 5, 0 },
+        { 0, 0, 0, 0, 0, 0, 0, 7, 4 },
+        { 0, 0, 5, 2, 0, 6, 3, 0, 0 } };
+    if (SolveSudoku(grid) == true)
+        printGrid(grid);
+    else
+        printf("No solution exists");
+
+    return 0;
+}