c: add functions to search for possabilities

the inBox, inCol, inRow functions search the 3x3 box, column, and row
of the index square given (i), for the possible number (n) given. If
the number is found in the box, column, or row, the number (n) is
skipped and another is tried until a possibility is found. If all
possibilities are exausted the 'solve()' function will backtrack.

The backtracking isn't emplemented yet.

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]);