d07

day07/d07p1.swift

@@ -0,0 +1,42 @@
+import Foundation
+
+struct Equation {
+    let left: Int
+    let right: [Int]
+
+    init(from s: String) {
+        let split = s.split(separator: " ")
+        left = Int(split[0].filter { $0 != ":" })!
+        right = split.dropFirst().map { Int($0)! }
+    }
+
+    func valid(with ops: [(Int, Int) -> Int]) -> Bool {
+        if ops.count != right.count - 1 {
+            return false
+        }
+        return left == ops.enumerated().reduce(right[0], { acc, op in
+            op.1(acc, right[op.0+1]) 
+        })
+    }
+}
+
+func readInput(_ filePath: String) throws -> [Equation] {
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    return content.split(separator: "\n").map { Equation(from: String($0)) }
+}
+
+func combo<T>(of symbols: [T], len: Int) -> [[T]] {
+    if len == 0 {
+        return [[]]
+    }
+    let cdrs = combo(of: symbols, len: len - 1)
+    return symbols.flatMap { s in cdrs.map { cdr in [s] + cdr } }
+}
+
+let op: [(Int, Int) -> Int] = [(+), (*)]
+let eqs = try readInput(CommandLine.arguments[1])
+let answer = eqs
+    .filter { eq in
+        combo(of: op, len: eq.right.count - 1).contains { eq.valid(with: $0) }
+    }.reduce(0, { s, eq in s + eq.left })
+print(answer)