1 files changed, 48 insertions, 2 deletions

diff --git a/c/sudoku.c b/c/sudoku.c
index 040ba8d..072d957 100644
--- a/c/sudoku.c
+++ b/c/sudoku.c
@@ -1,6 +1,44 @@
+#include <stdbool.h>
 #include <stdio.h>
 
 
+bool inBox(int i, int n, char puzzle[])
+{
+  int boxRow = (i / 9 / 3) * 27;
+  int boxCol = ((i % 9) / 3) * 3;
+
+  for(int j = boxRow; j < boxRow + 27; j += 9) {
+    for(int k = boxCol; k < boxCol + 3; k++){
+      if(puzzle[j + k] - '0' == n)
+        return true;
+    }
+  }
+  return false;
+}
+
+
+bool inCol(int i, int n, char puzzle[])
+{
+  int col = i % 9;
+  for(int j = col; j < 81; j += 9) {
+    if(puzzle[j] - '0' == n)
+      return true;
+  }
+  return false;
+}
+
+
+bool inRow(int i, int n, char puzzle[])
+{
+  int row = i/9;
+  for(int j = row; j/9 <= row; j++) {
+    if(puzzle[j] - '0' == n)
+      return true;
+  }
+  return false;
+}
+
+
 char* solve(char puzzle[])
 {
 
@@ -11,8 +49,15 @@ char* solve(char puzzle[])
       goto next; // this square is answered
     }
 
-    // found an unanswered square
-    //printf("%d", puzzle[i] - '0');
+    for(int n=1; n<10; n++) {
+      if(inRow(i, n, puzzle) || inCol(i, n, puzzle) || inBox(i, n, puzzle))
+        continue;
+
+      puzzle[i] = n + '0';
+      return solve(puzzle);
+    }
+
+    // need to backtrack
 
   next:
     i++;
@@ -41,6 +86,7 @@ void display(char puzzle[])
 
 int main(int argc, char *argv[])
 {
+  display(argv[1]);
   for(int i=1; i < argc; i++) {
     char* puzzle = solve(argv[i]);