Add day 3

Makefile

@@ -1 +1,22 @@
 CXXFLAGS := -std=c++20 -O2 -Wall -Wextra
+
+sources := $(wildcard *.cc)
+progs := $(patsubst %.cc,%,$(sources))
+
+.PHONY: all
+all: $(progs)
+
+.PHONY: clean
+clean:
+	rm -f $(progs) $(progs:=_test.txt)
+
+.PHONY: test
+test: $(addprefix test-,$(progs))
+
+.PHONY: test-%
+test-%: %_test.txt
+	@test -f $*_output.txt && (diff -u $*_output.txt $<; rm -f $<)
+	@test -f $*_output.txt || cat $<
+
+$(progs:=_test.txt): %_test.txt: %
+	./$< $*_input.txt > $@

d01.cc

@@ -3,7 +3,8 @@
 #include <vector>
 using namespace std;
 
-int main(int argc, char *argv[]) {
+int main(int argc, char *argv[])
+{
     if (argc <= 1) return 1;
 
     vector<unsigned> numbers;

d02.cc

@@ -14,7 +14,8 @@ struct commands {
     int pos;
 };
 
-int main(int argc, char *argv[]) {
+int main(int argc, char *argv[])
+{
     if (argc <= 1) return 1;
 
     vector<struct commands> commands;

d03.cc

@@ -0,0 +1,89 @@
+#include <iostream>
+#include <fstream>
+#include <vector>
+using namespace std;
+
+auto parse_input(char *file)
+{
+    ifstream input(file);
+    if (!input.is_open()) exit(1);
+
+    vector<string> parsed;
+    for (string line; getline(input, line);) {
+        parsed.push_back(line);
+    }
+    return parsed;
+}
+
+// Count the occurences of each bit position
+vector<int> count_occurences(vector<string> input)
+{
+    vector<int> counts(input[0].length(), 0);
+    for (string line : input) {
+        for (size_t i = 0; i < line.length(); i++) {
+            if (line[i] == '1') counts[i]++;
+            if (line[i] == '0') counts[i]--;
+        }
+    }
+    return counts;
+}
+
+unsigned part1(auto input)
+{
+    vector<int> counts = count_occurences(input);
+
+    // Convert the counts array into a binary value
+    unsigned out = 0;
+    for (int i : counts) {
+        out <<= 1;
+        if (i > 0) out += 1;
+    }
+
+    return out * (out ^ ((1 << counts.size()) - 1));
+}
+
+unsigned part2(auto input)
+{
+    size_t pos;
+
+    vector<string> numbers_ox = input;
+    pos = 0;
+    while (numbers_ox.size() > 1 && pos < input[0].length()) {
+        int count = count_occurences(numbers_ox)[pos];
+        char bit = (count >= 0) + '0';
+        for (size_t i = 0; i < numbers_ox.size(); i++) {
+            if (numbers_ox[i][pos] != bit) {
+                numbers_ox.erase(numbers_ox.begin()+i);
+                i--;
+            }
+        }
+        pos++;
+    }
+    unsigned ox = stol(numbers_ox[0], NULL, 2);
+
+    vector<string> numbers_co = input;
+    pos = 0;
+    while (numbers_co.size() > 1 && pos < input[0].length()) {
+        int count = count_occurences(numbers_co)[pos];
+        char bit = (count < 0) + '0';
+        for (size_t i = 0; i < numbers_co.size(); i++) {
+            if (numbers_co[i][pos] != bit) {
+                numbers_co.erase(numbers_co.begin()+i);
+                i--;
+            }
+        }
+        pos++;
+    }
+    unsigned co = stol(numbers_co[0], NULL, 2);
+
+    return ox * co;
+}
+
+int main(int argc, char *argv[])
+{
+    if (argc <= 1) return 1;
+    auto input = parse_input(argv[1]);
+
+    cout << part1(input) << endl;
+    cout << part2(input) << endl;
+}

d03_output.txt

@@ -0,0 +1,2 @@
+2595824
+2135254