Day 4 2024

1 files changed, 96 insertions, 0 deletions

diff --git a/2024/04/day04a.cpp b/2024/04/day04a.cpp
new file mode 100644
index 0000000..887ebef
--- /dev/null
+++ b/2024/04/day04a.cpp
@@ -0,0 +1,96 @@
+#include <algorithm>
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <vector>
+using namespace std;
+
+enum class Direction { U, D, R, L, UR, UL, DR, DL };
+Direction all_directions[] = {
+        Direction::U, Direction::D, Direction::R, Direction::L,
+        Direction::UR, Direction::UL, Direction::DR, Direction::DL
+};
+
+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);
+        case Direction::UR:
+                return make_pair(i-1, j+1);
+        case Direction::UL:
+                return make_pair(i-1, j-1);
+        case Direction::DR:
+                return make_pair(i+1, j+1);
+        case Direction::DL:
+                return make_pair(i+1, j-1);
+        }
+
+        return make_pair(-999,-999);
+}
+
+class Board {
+public:
+        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[N*i + j] = j < (int)lines[i].size() ?
+                                    lines[i][j] : out_of_bound;
+        }
+
+        string word_at(int i, int j, Direction d, int l) {
+                string ret = "";
+                auto p = make_pair(i, j);
+                for (int k = 0; k < l; k++, p = step(p, d))
+                        ret += (*this)[p];
+                return ret;
+        }
+
+        ~Board() {
+                delete []cells;
+        }
+
+private:
+        const char out_of_bound = '.';
+        char *cells;
+
+        char operator[](pair<int, int> p) {
+                auto [i, j] = p;
+                if (i >= N || i < 0 || j >= M || j < 0)
+                        return out_of_bound;
+                return cells[N*i + j];
+        }
+};
+
+int main() {
+        string line;
+        vector<string> lines;
+        while (getline(cin, line))
+                lines.push_back(line);
+
+        Board board(lines);
+        int tot = 0;
+        for (int i = 0; i < board.N; i++)
+                for (int j = 0; j < board.M; j++)
+                        for (Direction d : all_directions)
+                                if (board.word_at(i, j, d, 4) == "XMAS")
+                                        tot++;
+        cout << tot << endl;
+
+        return 0;
+}