Data commit

Task/String-matching/Erlang/string-matching.erl

@@ -0,0 +1,28 @@
+-module(character_matching).
+-export([starts_with/2,ends_with/2,contains/2]).
+
+%% Both starts_with and ends_with are mappings to 'lists:prefix/2' and
+%% 'lists:suffix/2', respectively.
+
+starts_with(S1,S2) ->
+    lists:prefix(S2,S1).
+
+ends_with(S1,S2) ->
+    lists:suffix(S2,S1).
+
+contains(S1,S2) ->
+    contains(S1,S2,1,[]).
+
+%% While S1 is at least as long as S2 we check if S2 is its prefix,
+%% storing the result if it is. When S1 is shorter than S2, we return
+%% the result. NB: this will work on any arbitrary list in erlang
+%% since it makes no distinction between strings and lists.
+contains([_|T]=S1,S2,N,Acc) when length(S2) =< length(S1) ->
+    case starts_with(S1,S2) of
+        true ->
+            contains(T,S2,N+1,[N|Acc]);
+        false ->
+            contains(T,S2,N+1,Acc)
+    end;
+contains(_S1,_S2,_N,Acc) ->
+    Acc.