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Task/Sorting-algorithms-Merge-sort/Nim/sorting-algorithms-merge-sort.nim

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+proc merge[T](a, b: var openarray[T], left, middle, right) =
+  let
+    leftLen = middle - left
+    rightLen = right - middle
+  var
+    l = 0
+    r = leftLen
+
+  for i in left .. <middle:
+    b[l] = a[i]
+    inc l
+  for i in middle .. < right:
+    b[r] = a[i]
+    inc r
+
+  l = 0
+  r = leftLen
+  var i = left
+
+  while l < leftLen and r < leftLen + rightLen:
+    if b[l] < b[r]:
+      a[i] = b[l]
+      inc l
+    else:
+      a[i] = b[r]
+      inc r
+    inc i
+
+  while l < leftLen:
+    a[i] = b[l]
+    inc l
+    inc i
+  while r < leftLen + rightLen:
+    a[i] = b[r]
+    inc r
+    inc i
+
+proc mergeSort[T](a, b: var openarray[T], left, right) =
+  if right - left <= 1: return
+
+  let middle = (left + right) div 2
+  mergeSort(a, b, left, middle)
+  mergeSort(a, b, middle, right)
+  merge(a, b, left, middle, right)
+
+proc mergeSort[T](a: var openarray[T]) =
+  var b = newSeq[T](a.len)
+  mergeSort(a, b, 0, a.len)
+
+var a = @[4, 65, 2, -31, 0, 99, 2, 83, 782]
+mergeSort a
+echo a