Day 3: Lobby ## Megathread guidelines - Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever) - You can send code in code blocks by using three backticks, the code, and then three backticks or use something such as https://topaz.github.io/paste/ if you prefer sending it through a URL ## FAQ - What is this?: Here is a post with a large amount of details: https://programming.dev/post/6637268 - Where do I participate?: https://adventofcode.com/ - Is there a leaderboard for the community?: We have a programming.dev leaderboard with the info on how to join in this post: https://programming.dev/post/6631465
Surprise, O(n^12) solutions don’t scale! But then it was delightful when the realization hit that the solution is actually very simple to implement - just keep removing the first digit that is followed by a higher one.
staticuint64_tjoltage(char *s, int len, int target) {
int i;
for (; len > target; len--) {
for (i=0; i<len-1 && s[i] >= s[i+1]; i++) ;
memmove(s+i, s+i+1, len-i);
}
return strtoul(s, NULL, 10);
}
intmain() {
char buf[1024];
uint64_t p1=0,p2=0;
int len;
while (fgets(buf, sizeof(buf), stdin)) {
for (len=0; isdigit(buf[len]); len++) ;
buf[len] = '\0';
p2 += joltage(buf, len, 12);
p1 += joltage(buf, 12, 2);
}
printf("03: %lu %lu\n", p1, p2);
}
I’m still having to finish yesterday’s x86-16 assembly implementation, for which I had to write some support code to deal with large numbers as strings. That will come in useful today, too!
C
Surprise, O(n^12) solutions don’t scale! But then it was delightful when the realization hit that the solution is actually very simple to implement - just keep removing the first digit that is followed by a higher one.
static uint64_t joltage(char *s, int len, int target) { int i; for (; len > target; len--) { for (i=0; i<len-1 && s[i] >= s[i+1]; i++) ; memmove(s+i, s+i+1, len-i); } return strtoul(s, NULL, 10); } int main() { char buf[1024]; uint64_t p1=0,p2=0; int len; while (fgets(buf, sizeof(buf), stdin)) { for (len=0; isdigit(buf[len]); len++) ; buf[len] = '\0'; p2 += joltage(buf, len, 12); p1 += joltage(buf, 12, 2); } printf("03: %lu %lu\n", p1, p2); }Repo link
I’m still having to finish yesterday’s x86-16 assembly implementation, for which I had to write some support code to deal with large numbers as strings. That will come in useful today, too!