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
|
#include <iostream>
#include <algorithm>
#include <string>
#include <string_view>
#include <vector>
using namespace std;
enum class Direction { U, D, R, L };
Direction all_directions[] = {
Direction::U, Direction::D, Direction::R, Direction::L,
};
pair<int, int> step(pair<int, int> p, Direction d) {
auto [i, j] = p;
switch (d) {
case Direction::U:
return make_pair(i-1, j);
case Direction::D:
return make_pair(i+1, j);
case Direction::R:
return make_pair(i, j+1);
case Direction::L:
return make_pair(i, j-1);
}
return make_pair(-999,-999);
}
Direction turn(Direction d) {
switch (d) {
case Direction::U:
return Direction::R;
case Direction::D:
return Direction::L;
case Direction::R:
return Direction::D;
case Direction::L:
return Direction::U;
}
return Direction::U;
}
class Board {
public:
const char out_of_bound = '$';
int M, N;
Board(vector<string> &lines) {
N = lines.size();
M = 0;
for (string l : lines)
M = max(M, (int)l.size());
cells = new char[M * N];
for (int i = 0; i < N; i++)
for (int j = 0; j < M; j++)
cells[M*i + j] = j < (int)lines[i].size() ?
lines[i][j] : out_of_bound;
}
~Board() {
delete []cells;
}
char operator[](pair<int, int> p) {
int c = coord(p);
return c == -1 ? out_of_bound : cells[c];
}
bool is_obstruction(pair<int, int> p) {
return (*this)[p] == '#';
}
bool is_visited(pair<int, int> p) {
return (*this)[p] == 'x';
}
void set_visited(pair<int, int> p) {
int c = coord(p);
cells[c] = 'x';
}
private:
char *cells;
int coord(pair<int, int> p) {
auto [i, j] = p;
return i >= N || i < 0 || j >= M || j < 0 ? -1 : M*i + j;
}
};
Direction guard_direction(char c) {
switch (c) {
case '^':
return Direction::U;
case 'v':
return Direction::D;
case '>':
return Direction::R;
case '<':
return Direction::L;
}
return Direction::U;
}
pair<pair<int, int>, Direction> find_guard(Board &board) {
pair<int, int> p(0, 0);
for (p.first = 0; p.first < board.N; p.first++) {
for (p.second = 0; p.second < board.M; p.second++) {
if (board[p] != '.' && board[p] != '#') {
Direction d = guard_direction(board[p]);
return make_pair(p, d);
}
}
}
return make_pair(make_pair(-999, -999), Direction::U);
}
int main() {
string line;
vector<string> lines;
while (getline(cin, line))
lines.push_back(line);
Board board(lines);
int tot = 1;
auto [p, d] = find_guard(board);
board.set_visited(p);
while (true) {
auto q = step(p, d);
if (board[q] == board.out_of_bound)
break;
if (board.is_obstruction(q)) {
d = turn(d);
} else {
p = q;
if (!board.is_visited(p)) {
board.set_visited(p);
tot++;
}
}
}
cout << tot << endl;
return 0;
}
|
