Advent of code 2025 (not proud)
technoduck.me
1#include <stddef.h>
2#include <stdio.h>
3#include <stdlib.h>
4
5
6int get_acces(int** matrix,int i,int j,int last_i,int last_j) { // last_{i,j} are bools to indicate we are in the last row}
7 int neighbors = -1;
8 int i_0 = 0;
9 int i_last = 0;
10 int j_0= 0;
11 int j_last = 0;
12
13 if (i == 0) {
14i_0 = 1;
15 } else if (last_i) {
16
17i_last = 1;
18 }
19 if (j==0) {
20
21j_0 = 1;
22 } else if (last_j) {
23
24j_last = 1;
25 }
26
27 // for step 2 we will be working modulus 2. during the run, once we establish a roll as accesible it will get replaces with 3.
28 // while counting it for the neighbors it will still result in true for %2.
29 // once a run is over, we iterate over the whole matrix again and reduce all 3's by 1.
30 for (int ii = -1+i_0; ii<=1-i_last; ii++) {
31 for (int jj = -1+j_0; jj<=1-j_last ; jj++) {
32 if (matrix[i+ii][j+jj]%2) {
33 neighbors++;
34 }
35 }
36 }
37 if (neighbors<4) {
38 return 1;
39 } else {
40 return 0;
41 }
42}
43
44int main(int argc, char* argv[]) {
45
46
47 FILE* f = NULL;
48 char* line = NULL;
49 size_t size = 0;
50 ssize_t nread = 0;
51 int len = 0;
52 int w = 0;
53 int access = 0;
54 int accesible_rolls = 0;
55 int total_accesible_rolls = 0;
56
57 int** matrix_ptr = NULL;
58
59
60 f = fopen(argv[1], "r");
61
62
63 while ((nread = getline(&line, &size, f)) != -1) {
64 w = nread-2;
65 matrix_ptr = (int **)realloc(matrix_ptr, (len+1) * (nread-2)*sizeof(int));
66 matrix_ptr[len] = (int *)malloc((nread-2)*sizeof(int));
67 for (int i = 0; i< nread-1; i++) {
68 if (line[i] == '@') {
69 matrix_ptr[len][i] = 1;
70
71 } else {
72 matrix_ptr[len][i] = 0;
73 }
74 // printf("%d",(&matrix_ptr)[j][i]);
75 }
76 len++;
77 }
78
79 // just a matrix out of input.
80
81 //
82 // [(i-1,j-1)][(i-1,j)] [(i-1,j+1)]
83 // [(i,j-1)] [(i,j)] [(i,j+1)]
84 // [(i+1,j-1)][(i+1,j)] [(i+1,j+1)]
85 // check all of those in clockwise order
86 //
87
88 do {
89accesible_rolls=0;
90 for (int i = 0; i<len; i++) {
91 for (int j = 0; j<w+1; j++) {
92 if(matrix_ptr[i][j]==1) {
93 access = get_acces(matrix_ptr, i, j, (i==len-1), (j==w));
94 if (access) {
95 matrix_ptr[i][j]+=2;
96 accesible_rolls++;
97 printf("x");
98 }else {
99
100 printf("@");
101 }
102 } else {
103 printf(".");
104 }
105
106 }
107 printf("\n");
108 }
109
110
111 for (int i = 0; i<len; i++) {
112 for (int j = 0; j<w+1; j++) {
113 if(matrix_ptr[i][j]==3) {
114 matrix_ptr[i][j]--;
115
116 }
117 }}
118
119 printf("\n\n accesible rolls: %d\n",accesible_rolls);
120 total_accesible_rolls+=accesible_rolls;
121 }while (accesible_rolls>0);
122
123
124
125
126
127 printf("\n\n total accesible rolls: %d\n",total_accesible_rolls);
128
129
130 free(matrix_ptr);
131 free(f);
132 free(line);
133 return 0;
134}