Advent of code 2025 (not proud)
technoduck.me
1#include <math.h>
2#include <stdio.h>
3#include <stdlib.h>
4#include <string.h>
5
6
7int count_digit(unsigned long long num){
8 int len = 0;
9 while (num!=0) {
10 num /= 10;
11 len++;
12
13 }
14 return len;
15}
16
17int part_one_invalid(unsigned long long num) {
18 int answer = 0;
19
20 int len = count_digit(num);
21 if (len%2) {
22 answer = 0;
23 }
24
25 //it gonna be pair so no worry
26 unsigned long long halfer = pow(10, len/2);
27
28 if (num/halfer == num%halfer) {
29 answer = 1;
30 }
31 return answer;
32
33}
34
35
36int part_two_invalid(unsigned long long num) {
37 int answer = 0;
38 int len = count_digit(num);
39 int j;
40
41 for (int i =1; i<=len/2; i++) {
42 if (!((len%i)==0)) {
43 continue;
44 }
45 int chunk_num = len/i;
46 // use / and % to isolate chunks, with powers of 10 to the i
47 long long first = num % (long long)pow(10, i);
48
49 for (j = 1; j< chunk_num; j++) {
50 long long chunk = num % (long long)pow(10,i*(j+1))/ (long long)pow(10,i*j);
51 if (chunk != first) {
52 break;
53
54 }
55 }
56 if (j == chunk_num) {
57 answer=1;
58 }
59
60
61 }
62
63
64
65 return answer;
66}
67
68int main (int argc, char* argv[]) {
69
70 FILE* f = NULL;
71 char* line = NULL;
72
73 unsigned long long start = 0;
74 unsigned long long end = 0;
75 long long front_part = 0;
76 long long end_part = 0;
77 unsigned long long invalid_sum = 0;
78 ssize_t nlength;
79 size_t size = 0;
80
81 f = fopen(argv[1],"r");
82
83 while ((nlength = getdelim(&line, &size, ',', f) != -1)) {
84 start = atoll(strsep(&line, "-"));
85 end = atoll(strsep(&line, "-"));
86
87 printf("start: %llu ",start);
88 printf("end: %llu\n",end);
89
90
91
92
93 for (unsigned long long i = start; i<=end; i++) {
94
95
96
97 if (part_two_invalid(i)) {
98 invalid_sum += i;
99 printf("invalid number found: %llu\n",i);
100
101 }
102
103
104
105
106
107 }
108
109
110
111 }
112
113
114 printf("invalid sum: %llu", invalid_sum);
115
116
117 free(line);
118 free(f);
119 return 0;
120}