natecook1000 · September 20, 2018 22:35 · Sep 20, 2018
diff --git a/firstLiteralMatch.swift b/firstLiteralMatch.swift
@@ -0,0 +1,26 @@
+extension Collection where Element: Hashable {
+  /// Returns the first matching element in `needles`, along with its index.
+  func firstLiteralMatch<C: Collection>(from needles: C) -> (C.Element, Index)?
+    where C.Element: Collection, C.Element.Element == Element
+  {
+    let prefixes = Dictionary(grouping: needles, by: { $0.first! })
+    for i in indices {
+      if let possibleMatches = prefixes[self[i]] {
+        if let match = possibleMatches.first(where: { self[i...].starts(with: $0) }) {
+          return (match, i)
+        }
+      }
+    }
+    return nil
+  }
+}
+
+let text = """
+  Lorem ipsum dolor sit amet, consectetur adipiscing elit. \
+  Nullam a imperdiet magna. Quisque quis libero non risus \
+  commodo efficitur. Sed lorem urna, scelerisque sit \
+  amet porta eget, efficitur at libero. Ut a viverra augue.
+  """
+
+text.firstLiteralMatch(from: ["sit", "elit", "libero"])
+// ("sit", ...)