day9: part2 +30% efficiency increase

with caterpillar algorithm over brute force

day9/Makefile

@@ -21,6 +21,11 @@ CFLAGS+=-I$(INCLUDE)
 
 STRIP=strip
 
+DEFINES?=-DCATERPILLAR
+
+CFLAGS+= $(DEFINES)
+CXXFLAGS+= $(DEFINES)
+
 # Number of iterations to profile program
 PROF_ITERATIONS?=40
 # Set concurrent profiling runs to be number of *physical* cpu cores

day9/day9.c

@@ -72,6 +72,7 @@ inline static u64 ud_sort(size_t i, size_t j)
 
 	return slice[0] + slice[len-1];
 }
+#ifndef CATERPILLAR 
 static u64 find_set(u64 target)
 {
 	for(register size_t i =0;i<input_sz;i++)
@@ -90,6 +91,65 @@ static u64 find_set(u64 target)
 }
 #endif
 
+#ifdef CATERPILLAR 
+static int cp_outer_bounds(size_t low, size_t high, u64* restrict low0, u64* restrict high0)
+{
+	int mask = 0;
+	if(low) {
+		*low0 = input[low-1];
+		mask|=1;
+	}
+	if(high<input_sz-1) {
+		*high0 = input[high+1];
+		mask|=2;
+	}
+	return mask;
+}
+static u64 find_set_caterpillar(u64 target)
+{
+	u64 value;
+	size_t low, high;
+	low = high = 0;
+	while(1) {
+		if( (value = csum(low, high)) == target ) {
+			printf("%lu\n", ud_sort(low, high));
+			return 0;
+		}
+		else {
+			u64 blow, bhigh;
+			blow = bhigh=0;
+			if(value < target) {
+				// Add largest outer bound
+				switch(cp_outer_bounds(low, high, &blow, &bhigh))
+				{
+					case 0: goto fuck;
+					case 1: /* Lower bound is the only possible one to add */
+						low -= 1;
+						break;
+					case 2: /* Higher bound is the only possible one to add */
+						high += 1;
+						break;
+					case 3:
+						if(blow <= bhigh) high+=1;
+						else low -=1;
+				}	
+			} else if (value > target) {
+				// Remove smallest inner bount
+				blow = input[low];
+				bhigh =input[high];
+				if(blow <= bhigh) low += 1;
+				else high -=1;
+			}
+		}
+	}
+fuck:
+	fprintf(stderr, "No set found\n");
+	return 1;
+}
+#endif
+
+#endif
+
 int main()
 {
 	map_t def = map_new();
@@ -119,7 +179,13 @@ int main()
 	{
 		if(!result[i].valid && !(result[i].sum[0] | result[i].sum[1])) {
 #ifdef PART2
-			return find_set(result[i].num);
+			return
+#ifdef CATERPILLAR 
+			find_set_caterpillar
+#else
+			find_set
+#endif
+			(result[i].num);
 #else
 			printf("%lu\n", result[i].num);
 			return 0;