Data update

Task/String-matching/OCaml/string-matching.ml

@@ -0,0 +1,86 @@
+let match1 s1 s2 =
+  let len1 = String.length s1
+  and len2 = String.length s2 in
+  if len1 < len2 then false else
+    let sub = String.sub s1 0 len2 in
+    (sub = s2)
+
+(* testing in the top-level:
+
+ # match1 "Hello" "Hello World!" ;;
+ - : bool = false
+ # match1 "Hello World!" "Hello" ;;
+ - : bool = true
+*)
+
+let match2 s1 s2 =
+  let len1 = String.length s1
+  and len2 = String.length s2 in
+  if len1 < len2 then false else
+    let rec aux i =
+      if i < 0 then false else
+        let sub = String.sub s1 i len2 in
+        if (sub = s2) then true else aux (pred i)
+    in
+    aux (len1 - len2)
+
+(*
+ # match2 "It's raining, Hello World!" "umbrella" ;;
+ - : bool = false
+ # match2 "It's raining, Hello World!" "Hello" ;;
+ - : bool = true
+*)
+
+let match3 s1 s2 =
+  let len1 = String.length s1
+  and len2 = String.length s2 in
+  if len1 < len2 then false else
+    let sub = String.sub s1 (len1 - len2) len2 in
+    (sub = s2)
+
+(*
+ # match3 "Hello World" "Hello" ;;
+ - : bool = false
+ # match3 "Hello World" "World" ;;
+ - : bool = true
+*)
+
+let match2_loc s1 s2 =
+  let len1 = String.length s1
+  and len2 = String.length s2 in
+  if len1 < len2 then (false, -1) else
+    let rec aux i =
+      if i < 0 then (false, -1) else
+        let sub = String.sub s1 i len2 in
+        if (sub = s2) then (true, i) else aux (pred i)
+    in
+    aux (len1 - len2)
+
+(*
+ # match2_loc "The sun's shining, Hello World!" "raining" ;;
+ - : bool * int = (false, -1)
+ # match2_loc "The sun's shining, Hello World!" "shining" ;;
+ - : bool * int = (true, 10)
+*)
+
+let match2_num s1 s2 =
+  let len1 = String.length s1
+  and len2 = String.length s2 in
+  if len1 < len2 then (false, 0) else
+    let rec aux i n =
+      if i < 0 then (n <> 0, n) else
+        let sub = String.sub s1 i len2 in
+        if (sub = s2)
+        then aux (pred i) (succ n)
+        else aux (pred i) (n)
+    in
+    aux (len1 - len2) 0
+
+(*
+ # match2_num "This cloud looks like a camel, \
+     that other cloud looks like a llama" "stone" ;;
+ - : bool * int = (false, 0)
+ # match2_num "This cloud looks like a camel, \
+     that other cloud looks like a llama" "cloud" ;;
+ - : bool * int = (true, 2)
+*)