Added day 1 solution

day_1/part_1_sample.txt

@@ -0,0 +1,4 @@
+1abc2
+pqr3stu8vwx
+a1b2c3d4e5f
+treb7uchet

day_1/part_2_sample.txt

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+two1nine
+eightwothree
+abcone2threexyz
+xtwone3four
+4nineeightseven2
+zoneight234
+7pqrstsixteen

day_1/solution.d

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+module day_1.solution;
+
+import std.file;
+import std.string : splitLines;
+import std.algorithm;
+import std.stdio;
+import std.uni : isNumber;
+
+void part1() {
+    readText("part_1_input.txt")
+        .splitLines()
+        .map!((line) {
+            int a = -1, b = -1;
+            for (size_t i = 0; i < line.length; i++) {
+                if (a == -1 && isNumber(line[i])) a = line[i] - '0';
+                if (b == -1 && isNumber(line[$-i-1])) b = line[$-i-1] - '0';
+                if (a != -1 && b != -1) break;
+            }
+            return a * 10 + b;
+        })
+        .sum()
+        .writeln();
+}
+
+void part2() {
+    int findDigit(string s, size_t idx) {
+        if (isNumber(s[idx])) return s[idx] - '0';
+        const string[] words = ["one", "two", "three", "four", "five", "six", "seven", "eight", "nine"];
+        static foreach (size_t i, string word; words) {
+            if (s.length - idx >= word.length && s[idx .. idx + word.length] == word) {
+                return cast(int) i + 1;
+            }
+        }
+        return -1;
+    }
+
+    readText("part_2_input.txt")
+        .splitLines()
+        .map!((line) {
+            int a = -1, b = -1;
+            for (size_t i = 0; i < line.length; i++) {
+                int an = findDigit(line, i);
+                int bn = findDigit(line, line.length-i-1);
+                if (a == -1 && an != -1) a = an;
+                if (b == -1 && bn != -1) b = bn;
+                if (a != -1 && b != -1) break;
+            }
+            return a * 10 + b;
+        })
+        .sum()
+        .writeln();
+}
+
+void main() {
+    part1();
+    part2();
+}