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
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
|
#include <fstream>
#include <iostream>
#include <map>
#include <regex>
#include <set>
#include <tuple>
#include <vector>
using namespace std;
using pos_type = tuple<long, long>;
using velo_type = tuple<long, long>;
vector<tuple<pos_type, velo_type>>
read_file(string_view filename)
{
static const regex pattern{ R"(^p=(-?\d+),(-?\d+) v=(-?\d+),(-?\d+)$)" };
fstream input{ filename };
vector<tuple<pos_type, velo_type>> data;
for ( string line; getline(input, line); ) {
smatch matches;
if ( regex_search(line, matches, pattern) ) {
data.push_back({ { stoi(matches[1]), stoi(matches[2]) },
{ stoi(matches[3]), stoi(matches[4]) } });
}
}
return data;
}
/*
void
print(const vector<tuple<pos_type, velo_type>>& robots, long width, long height)
{
map<pos_type, long> map;
for ( const auto& [pos, velo]: robots ) {
map[pos]++;
}
for ( long y = 0; y != height; ++y ) {
for ( long x = 0; x != width; ++x ) {
auto pos = map.find({ x, y });
if ( pos != map.end() ) {
cout << pos->second;
}
else {
cout << '.';
}
}
cout << '\n';
}
cout << endl;
}
*/
/*
void
print_pic(const vector<tuple<pos_type, velo_type>>& robots, long width, long height)
{
map<pos_type, long> map;
for ( const auto& [pos, velo]: robots ) {
map[pos]++;
}
for ( long y = 0; y != height; ++y ) {
for ( long x = 0; x != width; ++x ) {
auto pos = map.find({ x, y });
cout << (pos != map.end() ? 'X' : ' ');
}
cout << '\n';
}
cout << endl;
}
*/
long
count(const vector<tuple<pos_type, velo_type>>& robots, long width, long height)
{
map<pos_type, long> map;
const auto width_half = width / 2;
const auto height_half = height / 2;
for ( const auto& [pos, velo]: robots ) {
const auto [x, y] = pos;
if ( x == width_half || y == height_half ) {
continue;
}
map[{ x / (width_half + 1), y / (height_half + 1) }]++;
}
long result = 1;
for ( const auto& [pos, count]: map ) {
result *= count;
}
return result;
}
void
move(vector<tuple<pos_type, velo_type>>& robots, long width, long height)
{
for ( auto& [pos, velo]: robots ) {
auto& [x, y] = pos;
auto [vx, vy] = velo;
x = (x + width + vx) % width;
y = (y + height + vy) % height;
}
}
void
part1(vector<tuple<pos_type, velo_type>> robots, long width, long height)
{
for ( long second = 0; second != 100; ++second ) {
move(robots, width, height);
}
cout << count(robots, width, height) << endl;
}
void
part2(vector<tuple<pos_type, velo_type>> robots, long width, long height)
{
auto min_result = numeric_limits<long>::max();
long second_found = 0;
for ( long second = 0; second != 100000; ++second ) {
auto result = count(robots, width, height);
if ( result < min_result ) {
second_found = second;
min_result = result;
}
move(robots, width, height);
}
cout << second_found << endl;
}
void
part2_alternative(vector<tuple<pos_type, velo_type>> robots, long width, long height)
{
set<pos_type> seen;
for ( long second = 0; second != 100000; ++second ) {
seen.clear();
bool overlap = false;
for ( const auto& [pos, velo]: robots ) {
if ( seen.contains(pos) ) {
overlap = true;
break;
}
seen.insert(pos);
}
if ( !overlap ) {
cout << second << endl;
break;
}
move(robots, width, height);
}
}
int
main()
{
#if 0
auto robots = read_file("data/day14-sample1.txt");
part1(robots, 11, 7);
#else
auto robots = read_file("data/day14.txt");
part1(robots, 101, 103);
part2(robots, 101, 103);
part2_alternative(robots, 101, 103);
#endif
}
|
