Top Down Merge Sort

Sort range [b,e) recursively

1. Find midpoint m of range 2. Sort [b,m) with recursive call 3. Sort [m,e) with recursive call 4. Merge ranges [b,m) and [m,e) to [b,e)

divide here (m = 10/2 = 5) | [0,10) = [20 10 40 50 20 90 10 80 70] [0,5) = [20 10 40 50 20] -> [10 20 20 40 50] [5,10) = [90 10 80 70] -> [10 70 80 90] [0,10) = [10 10 20 20 40 50 70 80 90]

• Stable
• Runtime = Θ(n log n)
• Runspace = +Θ(n)
• No way around +Θ(n) runspace for arrays, vectors, deques