From 4797abb8b2cf72858ad7c5369a2a8c76da3db48c Mon Sep 17 00:00:00 2001
From: Aadit Agrawal <tech@aaditagrawal.com>
Date: Tue, 29 Oct 2024 11:26:12 +0530
Subject: [PATCH] Add DS/C/test/sudoku.c

---
 DS/C/test/sudoku.c | 101 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)
 create mode 100644 DS/C/test/sudoku.c

diff --git a/DS/C/test/sudoku.c b/DS/C/test/sudoku.c
new file mode 100644
index 0000000..b44cda2
--- /dev/null
+++ b/DS/C/test/sudoku.c
@@ -0,0 +1,101 @@
+#include <stdio.h>
+#include <stdbool.h>
+
+#define N 9
+
+// printf function
+void printBoard(int board[N][N]) {
+    for (int i = 0; i < N; i++) {
+        for (int j = 0; j < N; j++) {
+            printf("%d ", board[i][j]);
+        }
+        printf("\n");
+    }
+}
+
+// if placing num at board[row][col] is valid
+bool isValid(int board[N][N], int row, int col, int num) {
+    // Check row
+    for (int x = 0; x < N; x++)
+        if (board[row][x] == num)
+            return false;
+
+    // Check column
+    for (int x = 0; x < N; x++)
+        if (board[x][col] == num)
+            return false;
+
+    // Check grid
+    int startRow = row - row % 3;
+    int startCol = col - col % 3;
+    for (int i = 0; i < 3; i++)
+        for (int j = 0; j < 3; j++)
+            if (board[i + startRow][j + startCol] == num)
+                return false;
+
+    return true;
+}
+
+// solve Sudoku using backtracking
+bool solveSudoku(int board[N][N]) {
+    int row, col;
+    bool emptyFound = false;
+
+    // Find the next empty cell
+    for (row = 0; row < N; row++) {
+        for (col = 0; col < N; col++) {
+            if (board[row][col] == 0) {
+                emptyFound = true;
+                break;
+            }
+        }
+        if (emptyFound)
+            break;
+    }
+
+    // No empty cell left, puzzle solved
+    if (!emptyFound)
+        return true;
+
+    // Try placing digits 1-9
+    for (int num = 1; num <= N; num++) {
+        if (isValid(board, row, col, num)) {
+            board[row][col] = num;
+
+            if (solveSudoku(board))
+                return true;
+
+            // Undo if not valid
+            board[row][col] = 0;
+        }
+    }
+
+    return false; // No sol found
+}
+
+int main() {
+    int board[N][N];
+
+    // enter the board values
+    printf("Enter the Sudoku board values (use 0 for empty cells):\n");
+    for (int i = 0; i < N; i++) {
+        for (int j = 0; j < N; j++) {
+            printf("Enter value for cell [%d][%d]: ", i + 1, j + 1);
+            scanf("%d", &board[i][j]);
+            // error handling included
+            if (board[i][j] < 0 || board[i][j] > 9) {
+                printf("Invalid input. Please enter a number between 0 and 9.\n");
+                j--; // Retry current cell
+            }
+        }
+    }
+
+    if (solveSudoku(board)) {
+        printf("\nSolved Sudoku:\n");
+        printBoard(board);
+    } else {
+        printf("No solution exists\n");
+    }
+
+    return 0;
+}