1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
|
#include <fstream>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <vector>
using namespace std;
using pos_type = tuple<size_t, size_t>;
using area_type = set<pos_type>;
using areas_type = vector<area_type>;
map<pos_type, char>
read_file(string_view filename)
{
fstream input{ filename };
map<pos_type, char> data;
size_t yPos = 0;
for ( string line; getline(input, line); ) {
for ( size_t xPos = 0; xPos != line.size(); ++xPos ) {
data[{ xPos, yPos }] = line.at(xPos);
}
++yPos;
}
return data;
}
constexpr vector<pos_type>
neighbors(pos_type pos)
{
const auto [x, y] = pos;
return { { x - 1, y }, { x, y - 1 }, { x + 1, y }, { x, y + 1 } };
}
areas_type
areas(map<pos_type, char> data)
{
auto find_area = [&](pos_type start) {
set<pos_type> area;
queue<pos_type> queue;
queue.push(start);
const auto digit = data.at(start);
while ( !queue.empty() ) {
auto pos = queue.front();
queue.pop();
if ( !data.contains(pos) ) {
continue;
}
for ( const auto& neighbor: neighbors(pos) ) {
if ( !data.contains(neighbor) ) {
continue;
}
if ( data.at(neighbor) != digit ) {
continue;
}
queue.push(neighbor);
}
area.insert(pos);
data.erase(pos);
}
return area;
};
areas_type areas;
while ( !data.empty() ) {
auto area = find_area(data.begin()->first);
areas.push_back(area);
}
return areas;
}
size_t
count_edges(const set<pos_type>& area)
{
size_t sum = 0;
for ( const auto& pos: area ) {
for ( const auto& neighbor: neighbors(pos) ) {
if ( !area.contains(neighbor) ) {
++sum;
}
}
}
return sum;
}
size_t
count_common_sides(const set<pos_type>& area)
{
size_t count = 0;
for ( const auto& [x, y]: area ) {
if ( area.contains({ x - 1, y }) ) {
for ( const auto y2: { y - 1, y + 1 } ) {
if ( !area.contains({ x, y2 }) && !area.contains({ x - 1, y2 }) ) {
++count;
}
}
}
if ( area.contains({ x, y - 1 }) ) {
for ( const auto x2: { x - 1, x + 1 } ) {
if ( !area.contains({ x2, y }) && !area.contains({ x2, y - 1 }) ) {
++count;
}
}
}
}
return count;
}
void
part1(const map<pos_type, char>& data)
{
size_t sum = 0;
for ( const auto& area: areas(data) ) {
auto edges = count_edges(area);
sum += area.size() * edges;
}
cout << sum << endl;
}
void
part2(const map<pos_type, char>& data)
{
size_t sum = 0;
for ( const auto& area: areas(data) ) {
auto edges = count_edges(area);
auto common_sides = count_common_sides(area);
sum += area.size() * (edges - common_sides);
}
cout << sum << endl;
}
int
main()
{
auto data = read_file("data/day12.txt");
part1(data);
part2(data);
}
|
