diff --git a/solve.c b/solve.c
index cdc7b22..a0d1420 100644
--- a/solve.c
+++ b/solve.c
@@ -20,89 +20,34 @@
 
 #include <stdio.h>
 
-struct match {
-	unsigned row;
-	unsigned col;
-	unsigned val;
-};
-
-struct cellref {
-	unsigned row, col;
-	struct cellstate *state;
-};
-
-enum apply_res { ERROR, NO_MATCH, MATCH };
-
-typedef struct cellref cellgroup[NDIGITS];
-typedef bool (*rulefn)(cellgroup *group, struct match *match_out);
-
-static bool one_place_for_digit(cellgroup *group, struct match *match_out)
-{
-	for (unsigned val = 0; val < NDIGITS; ++val) {
-		unsigned n = 0, row = NDIGITS, col = NDIGITS;
-		for (unsigned i = 0; i < NDIGITS; ++i) {
-			if (!(*group)[i].state->det && (*group)[i].state->pvals[val]) {
-				row = (*group)[i].row;
-				col = (*group)[i].col;
-				++n;
-				if (n > 1)
-					break;
-			}
-		}
-
-		if (n == 1) {
-			match_out->row = row;
-			match_out->col = col;
-			match_out->val = val;
-			return true;
-		}
-	}
-
-	return false;
-}
-
-static const rulefn rules[] = {
-	&one_place_for_digit,
-};
-static const unsigned nrules = sizeof(rules) / sizeof(rules[0]);
-
-static enum apply_res apply_rules(struct sudoku *sud, cellgroup *group)
-{
-	struct match m;
-	bool matched = false;
-	for (unsigned i = 0; i < nrules; ++i) {
-		if (!rules[i](group, &m))
-			continue;
-		if (!update(sud, m.row, m.col, m.val))
-			return ERROR;
-		matched = true;
-	}
-	return matched ? MATCH : NO_MATCH;
-}
-
 int solve(struct sudoku *sud)
 {
-	cellgroup group = { 0 };
-	unsigned r, c, n;
+	unsigned r, c, n, val, np, pr, pc;
 	bool match;
-	enum apply_res res;
 
 	for (n = 0;; ++n) {
 		match = false;
 
-		/* Apply rules to each row. */
+		/* Check if only one place a value can go on each row. */
 		for (r = 0; r < NDIGITS; ++r) {
-			for (c = 0; c < NDIGITS; ++c) {
-				group[c].row = r;
-				group[c].col = c;
-				group[c].state = &sud->cells[r][c];
-			}
+			for (val = 0; val < NDIGITS; ++val) {
+				np = 0;
+				for (c = 0; c < NDIGITS; ++c) {
+					if (!sud->cells[r][c].det && sud->cells[r][c].pvals[val]) {
+						pr = r;
+						pc = c;
+						++np;
+						if (np > 1)
+							break;
+					}
+				}
 
-			res = apply_rules(sud, &group);
-			if (res == ERROR)
-				return -1;
-			else if (res == MATCH)
-				match = true;
+				if (np == 1) {
+					if (update(sud, pr, pc, val) != OK)
+						return -1;
+					match = true;
+				}
+			}
 		}
 
 		/* Exit if no matches. */