Added day 3.

source/app.d

@@ -3,7 +3,8 @@ import std.stdio;
 import day1.part1;
 import day1.part2;
 import day2.part1and2;
+import day3.part1;
 
 void main() {
-	dive2();
+	binaryDiagnostic2();
 }

source/day3/part1.d

@@ -0,0 +1,88 @@
+module day3.part1;
+
+import std.file;
+import std.stdio;
+import std.bitmanip;
+
+void writeBinary(uint n) {
+    for (int i = 31; i >= 0; i--) {
+        uint b = (n & (1 << i)) > 0 ? 1 : 0;
+        writef("%d ", b);
+    }
+    writeln();
+}
+
+void binaryDiagnostic() {
+    auto f = File("source/day3/input.txt", "r");
+    int[ubyte] frequencies;
+    int count = 0;
+    foreach (line; f.byLine) {
+        count++;
+        ubyte idx = 0;
+        foreach (c; line) {
+            if (idx !in frequencies) frequencies[idx] = 0;
+            if (c == '1') frequencies[idx]++;
+            idx++;
+        }
+    }
+    ulong bitCount = frequencies.length;
+    uint gamma = 0;
+    uint epsilon = 0;
+    foreach (idx, freq; frequencies) {
+        if (freq > count / 2) {
+            gamma |= (1 << (bitCount - 1 - idx));
+        } else {
+            epsilon |= (1 << (bitCount - 1 - idx));
+        }
+    }
+    writefln("Gamma: %d, Epsilon: %d, Power: %d", gamma, epsilon, gamma * epsilon);
+}
+
+bool is1Common(uint[] values, int idx, int bitCount, bool type) pure {
+    int count = 0;
+    foreach (v; values) {
+        if ((v & (1 << (bitCount - 1 - idx))) > 0) count++;
+    }
+    if (type) {
+        return count >= (values.length - count);
+    } else {
+        return count < (values.length - count);
+    }
+}
+
+void filter(ref uint[] values, int idx, int bitCount, bool type) pure {
+    bool common = is1Common(values, idx, bitCount, type);
+    uint[] newValues = [];
+    foreach (v; values) {
+        bool b = (v & (1 << (bitCount - 1 - idx))) > 0;
+        if (b == common) newValues ~= v;
+    }
+    values = newValues;
+}
+
+uint findValue(uint[] values, int bitCount, bool type) {
+    int idx = 0;
+    while (values.length > 1) {
+        filter(values, idx++, bitCount, type);
+    }
+    return values[0];
+}
+
+void binaryDiagnostic2() {
+    auto f = File("source/day3/input.txt", "r");
+    uint[] values = [];
+    int bitCount = 0;
+    foreach (line; f.byLine) {
+        bitCount = cast(int) line.length;
+        int idx = 0;
+        uint value = 0;
+        foreach (c; line) {
+            if (c == '1') value |= (1 << line.length - 1 - idx);
+            idx++;
+        }
+        values ~= value;
+    }
+    uint o2 = findValue(values, bitCount, true);
+    uint co2 = findValue(values, bitCount, false);
+    writefln("Oxygen: %d, CO2: %d, LS Rating: %d", o2, co2, o2 * co2);
+}

source/day3/test_input.txt

@@ -0,0 +1,12 @@
+00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010