implement bin-vec (vector that always stores its elements in order, for binary search)

fcore/bin-vec.sml

@@ -0,0 +1,120 @@
+signature BIN_VEC =
+sig
+  (* char is just 8 bits, which is smaller than int's 32 bits 
+   * and smaller = faster here*)
+  type elem = char
+  type t = char vector
+
+  val singleton: elem -> t
+  val getIndex: t * elem -> int
+  val insert: t * elem -> t
+end
+
+structure BinVec: BIN_VEC =
+struct
+  type elem = char
+  type t = char vector
+
+  fun singleton x = Vector.fromList [x]
+
+  fun helpFind (findNum, vec, low, high) =
+    if high >= low then
+      let
+        val mid = low + ((high - low) div 2)
+        val curNum = Vector.sub (vec, mid)
+      in
+        if curNum = findNum then mid
+        else if curNum < findNum then helpFind (findNum, vec, mid + 1, high)
+        else helpFind (findNum, vec, low, mid - 1)
+      end
+    else
+      ~1
+
+  fun getIndex (vec: t, findNum: elem) =
+    helpFind (findNum, vec, 0, Vector.length vec - 1)
+
+  fun reverseLinearSearch (pos, findNum, vec) =
+    if pos < 0 then
+      ~1
+    else
+      let
+        val curNum = Vector.sub (vec, pos)
+      in
+        if findNum > curNum then pos + 1
+        else reverseLinearSearch (pos - 1, findNum, vec)
+      end
+
+  fun forwardLinearSearch (pos, findNum, vec) =
+    if pos = Vector.length vec then
+      Vector.length vec
+    else
+      let
+        val curNum = Vector.sub (vec, pos)
+      in
+        if findNum > curNum then pos
+        else forwardLinearSearch (pos + 1, findNum, vec)
+      end
+
+  fun helpFindInsPos (findNum, vec, low, high, prevMid) =
+    if high >= low then
+      let
+        val mid = low + ((high - low) div 2)
+        val curNum = Vector.sub (vec, mid)
+      in
+        if curNum = findNum then
+          mid
+        else if curNum < findNum then
+          helpFindInsPos (findNum, vec, mid + 1, high, mid)
+        else
+          helpFindInsPos (findNum, vec, low, mid - 1, mid)
+      end
+    else
+      let
+        val curNum = Vector.sub (vec, prevMid)
+      in
+        if findNum < curNum then forwardLinearSearch (prevMid, findNum, vec)
+        else reverseLinearSearch (prevMid, findNum, vec)
+      end
+
+  fun findInsPos (findNum, vec) =
+    if Vector.length vec = 0 then ~1
+    else helpFindInsPos (findNum, vec, 0, Vector.length vec - 1, 0)
+
+  fun insert (vec: t, elem: elem) =
+    let
+      val insPos = findInsPos (elem, vec)
+    in
+      if insPos < 0 then
+        Vector.concat [Vector.fromList [elem], vec]
+      else if insPos = Vector.length vec then
+        Vector.concat [vec, Vector.fromList [elem]]
+      else
+        let
+          val elem = Vector.fromList [elem]
+          val elem = VectorSlice.full elem
+
+          val s2len = Vector.length vec - insPos
+          val slice1 = VectorSlice.slice (vec, 0, SOME insPos)
+          val slice2 = VectorSlice.slice (vec, insPos, SOME s2len)
+        in
+          VectorSlice.concat [slice1, elem, slice2]
+        end
+    end
+
+  fun delete (vec, elem) =
+    let
+      val insPos = findInsPos (elem, vec)
+    in
+      if insPos < 0 orelse insPos = Vector.length vec then
+        vec
+      else
+        let
+          val slice1 = VectorSlice.slice (vec, 0, SOME insPos)
+
+          val slice2Len = Vector.length vec - insPos - 1
+          val slice2 = VectorSlice.slice (vec, insPos + 1, SOME slice2Len)
+        in
+          VectorSlice.concat [slice1, slice2]
+        end
+    end
+end