107 lines
3.4 KiB
C
107 lines
3.4 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdbool.h>
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#include <ctype.h>
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#define MAP_SIZE 140
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typedef struct{
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int x, y;
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int width;
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int value;
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}NumberBox;
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char map[MAP_SIZE*MAP_SIZE] = {0};
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bool touching_symbol[MAP_SIZE*MAP_SIZE] = {false};
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NumberBox number_boxes[10000] = {0};
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bool is_touching_symbol( int x, int y) {
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for( int test_y=y-1; test_y<=y+1; test_y ++ ) {
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for( int test_x=x-1; test_x<=x+1; test_x ++ ) {
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if( test_y < 0 || test_x < 0 || test_y >= MAP_SIZE || test_x >= MAP_SIZE) continue;
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char c = map[ test_y*MAP_SIZE+test_x];
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if( !isdigit(c) && c != '.') {
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return true;
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}
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}
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}
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return false;
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}
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int main()
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{
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FILE *fp = fopen( "./input", "r");
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char line[256];
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int y = 0;
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while ( fgets( line, 256, fp ) != NULL) {
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memcpy( &map[MAP_SIZE*y++], line, MAP_SIZE );
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}
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int all_sum = 0;
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int schematic_sum = 0;
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int num_number_boxes = 0;
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for( int y=0; y<MAP_SIZE; y++ ) {
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char* read_pos = &map[y*MAP_SIZE];
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char* next_line = &map[(y+1)*MAP_SIZE];
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for( ;; ) {
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char* num_start = strpbrk( read_pos, "0123456789");
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if( num_start >= next_line || num_start == NULL ) break;
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char* num_end = num_start + strspn( num_start, "0123456789");
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if( num_end > next_line) num_end = next_line;
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// Extract the number
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char number_string[ 64] = {0};
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strncpy( number_string, num_start, num_end-num_start);
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int value = atoi( number_string );
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int x = num_start-&map[y*MAP_SIZE];
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int width = num_end - num_start;
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// Store the number box for the next part of the problem
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NumberBox nb = {x,y, width, value};
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number_boxes[ num_number_boxes++ ] = nb;
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// Are any of the digits touching a symbol
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bool is_touching = false;
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for( int x_pos=x; x_pos<x+width; x_pos++ ) {
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is_touching |= is_touching_symbol( x_pos, y);
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}
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if( is_touching ) schematic_sum += value;
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if( is_touching ) {
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// printf("%d, col: %d row: %d\n", value, x, y);
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}
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all_sum += value;
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read_pos = num_end;
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}
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}
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printf( "\nSum of schematic numbers: %d", schematic_sum);
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// Part 2
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int sum_of_gear_ratios = 0;
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for( int y=0; y<MAP_SIZE; y++ ) {
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for( int x=0; x<MAP_SIZE; x++ ) {
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if( map[y*MAP_SIZE+x] == '*') {
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// Found gear, find any touching numbers
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int num_touching = 0;
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int ratio = 1;
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for( int n_box=0; n_box<num_number_boxes; n_box++ ) {
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if( number_boxes[ n_box].x -1 <= x && number_boxes[ n_box].y -1 <=y &&
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(number_boxes[ n_box].x + number_boxes[ n_box].width)>= x && number_boxes[ n_box].y >=y ) {
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ratio *= number_boxes[n_box].value;
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printf("%d *", number_boxes[n_box].value, ratio);
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num_touching ++;
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}
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}
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if( num_touching >= 2) {
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printf(" + %d", sum_of_gear_ratios);
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sum_of_gear_ratios += ratio;
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printf(" = %d\n", sum_of_gear_ratios);
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}
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}
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}
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}
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printf( "\nSum of gear ratios: %d\n", sum_of_gear_ratios);
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}
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