day 3 part 1

4 files changed, 95 insertions, 1 deletions

diff --git a/.gitignore b/.gitignore
index e427dd8..8225d36 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1 @@
-*/input.txt
+*/*.txt
diff --git a/03/.gitignore b/03/.gitignore
new file mode 100644
index 0000000..ba2906d
--- /dev/null
+++ b/03/.gitignore
@@ -0,0 +1 @@
+main
diff --git a/03/main.cc b/03/main.cc
new file mode 100644
index 0000000..b452c95
--- /dev/null
+++ b/03/main.cc
@@ -0,0 +1,89 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+const vector<char> SYMBOLS = {'#', '$', '%', '&', '*', '+', '-', '/', '=', '@'};
+const vector<char> NUMBERS = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};
+
+int main() {
+	// phase 1 -- read lines into buffer
+	vector<string> lines;
+	for (string line; getline(cin, line);)
+		lines.push_back(line);
+	size_t rows = lines.size();
+	size_t cols = lines[0].size();
+
+	// phase 2 -- create valid number mask
+	vector<vector<bool>> valid_mask(rows, vector<bool>(cols, false));
+	for (int i = 0; i < rows; i++) {
+		for (int j = 0; j < cols; j++) {
+			// row and column offset for checking diagonals too
+			for (int roff = -1; roff <= 1; roff++) {
+				for (int coff = -1; coff <= 1; coff++) {
+					// skip any x,y coordinates that are outide the "grid"
+					int y = i + roff;
+					if (y < 0) continue;
+					if (y >= rows) continue;
+					int x = j + coff;
+					if (x < 0) continue;
+					if (x >= cols) continue;
+
+					for (char symbol : SYMBOLS)
+						if (lines[y][x] == symbol)
+							valid_mask[i][j] = true;
+				}
+			}
+		}
+	}
+
+	for (int i = 0; i < rows; i++) {
+		for (int j = 0; j < cols; j++)
+			printf("%c", lines[i][j]);
+		printf("\n");
+	}
+	for (int i = 0; i < rows; i++) {
+		for (int j = 0; j < cols; j++)
+			printf("%c", valid_mask[i][j] ? 'x' : ' ');
+		printf("\n");
+	}
+
+	// phase 3 -- read each number and add to output if any of its digits are
+	//            true in valid_mask
+	int output = 0;
+	int digit = 0;
+	int valid_digit = false;
+	for (int i = 0; i < rows; i++) {
+		for (int j = 0; j < cols; j++) {
+			char cell = lines[i][j];
+			bool valid = valid_mask[i][j];
+			int last_digit = digit;
+			for (char num : NUMBERS) {
+				if (cell != num)
+					continue;
+
+				// printf("[%c]", cell);
+				digit *= 10;
+				digit += cell - '0';
+				if (valid)
+					valid_digit = true;
+			}
+			if (digit == last_digit && digit != 0) {
+				// printf(" (inline, %d, %s)\n", digit, valid_digit ? "valid" : "not valid");
+				if (valid_digit)
+					output += digit;
+				digit = 0;
+				valid_digit = false;
+			}
+		}
+		if (digit != 0) {
+			// printf(" (EOL, %d, %s)\n", digit, valid_digit ? "valid" : "not valid");
+			if (valid_digit)
+				output += digit;
+			digit = 0;
+			valid_digit = false;
+		}
+	}
+
+	printf(">> %d\n", output);
+
+	return 0;
+}
diff --git a/03/makefile b/03/makefile
new file mode 100644
index 0000000..a78e3da
--- /dev/null
+++ b/03/makefile
@@ -0,0 +1,4 @@
+main: main.cc
+clean:
+	$(RM) main
+