Make fill proportion a parameter to gen()

sud.c

@@ -22,9 +22,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-#define REM_PROB_NUMER 2
-#define REM_PROB_DENOM 3
-
 #define MAX_FILL_ATTEMPTS 32
 
 static void initposs(struct sudoku *sud)
@@ -76,7 +73,7 @@ static void clear(struct sudoku *sud, unsigned r, unsigned c)
 	}
 }
 
-void gen(struct sudoku *sud)
+void gen(struct sudoku *sud, double fill_prop)
 {
 	/* Generate a completed sudoku. */
 retry:
@@ -93,10 +90,10 @@ retry:
 		}
 	}
 
-	/* Remove cells with probability of `1 / REMOVE_PROB_RECIP`. */
+	/* Remove cells with probability of 1 - fill_prop. */
 	for (unsigned r = 0; r < NDIGITS; ++r) {
 		for (unsigned c = 0; c < NDIGITS; ++c) {
-			if (rand() % REM_PROB_DENOM < REM_PROB_NUMER)
+			if ((double)rand() / (double)RAND_MAX < 1 - fill_prop)
 				clear(sud, r, c);
 		}
 	}