Add count functions

src/exam01/questions.sml

@@ -0,0 +1,38 @@
+
+
+(* Question n *)
+fun insert comp add li =
+  let
+    fun getLeft comp add li = foldr (fn (cur, acc) => if comp(cur, add) then cur::acc else acc) [] li
+    fun getRight comp add li = foldr (fn (cur, acc) => if comp(add, cur) then cur::acc else acc) [] li
+    val left = getLeft comp add li
+    val right = getRight comp add li
+  in
+    left @ [add] @ right
+  end;
+
+val res = insert (op <=) 4 [1,2,3,5,6];
+
+(* Question n *)
+fun countGreaterThan p li = foldl (fn (cur, acc) => if cur > p then 1 + acc else acc) 0 li;
+
+val res2 = countGreaterThan 4 [1,2,3,4,5,6]; (* shuold be 2 *)
+
+(* Question n *)
+fun countDups([]) = 0
+  | countDups([_]) = 0
+  | countDups(x::y::li) =
+    if x = y
+    then 1 + countDups(li)
+    (* Forget to prepend y back if no duplicate *)
+    else countDups(li); (* Should be: else countDups(y::li) *)
+
+val res3 = countDups([1,1,1,2,2,3,3,4,5,6]) (* should be 3 *)
+
+
+(* Question n *)
+fun countChars li = foldl (fn (cur, acc) => acc + length(explode(cur))) 0 li;
+
+val res4 = countChars ["123", "456", "789", "1"]; (* should be 10 *)
+
+