June 2018 Update

Task/Sorting-algorithms-Merge-sort/Julia/sorting-algorithms-merge-sort.julia

@@ -1,42 +1,27 @@
-function mergesort!(A::AbstractVector)
-    if length(A) <= 1
-        return A
-    end
-    middle = div(length(A), 2)
-    left = mergesort(A[1:middle])
-    right = mergesort(A[middle + 1:end])
-    result = Array(eltype(left), length(left) + length(right))
-    idx = 1
-    @inbounds while !isempty(left) && !isempty(right)
-        if left[1] <= right[1]
-            result[idx] = left[1]
-            left = left[2:end]
+function mergesort(arr::Vector)
+    if length(arr) ≤ 1 return arr end
+    mid = length(arr) ÷ 2
+    lpart = mergesort(arr[1:mid])
+    rpart = mergesort(arr[mid+1:end])
+    rst = similar(arr)
+    i = ri = li = 1
+    @inbounds while li ≤ length(lpart) && ri ≤ length(rpart)
+        if lpart[li] ≤ rpart[ri]
+            rst[i] = lpart[li]
+            li += 1
         else
-            result[idx] = right[1]
-            right = right[2:end]
+            rst[i] = rpart[ri]
+            ri += 1
         end
-        idx += 1
+        i += 1
     end
-    @inbounds while !isempty(left)
-        result[idx] = left[1]
-        left = left[2:end]
-        idx += 1
+    if li ≤ length(lpart)
+        copy!(rst, i, lpart, li)
+    else
+        copy!(rst, i, rpart, ri)
     end
-    @inbounds while !isempty(right)
-        result[idx] = right[1]
-        right = right[2:end]
-        idx += 1
-    end
-    for i=1:length(A)
-        A[i] = result[i]
-    end
-    return A
+    return rst
 end
 
-function mergesort(A::AbstractVector)
-    return mergesort!(copy(A))
-end
-
-A = randcycle(10)
-println("unsorted: ", A)
-println("sorted:   ", mergesort(A))
+v = rand(-10:10, 10)
+println("# unordered: $v\n -> ordered: ", mergesort(v))