Retrieving the top 100 numbers from one hundred million of numbers

Question

One of my friend has been asked with a question

Retrieving the max top 100 numbers from one hundred million of numbers

in a rece

Answer 1

There's no reason to sort the whole list. This should be doable in O(n) time. In pseudocode:

List top = new List

for each num in entireList
    for i = 0 to top.Length
        if num > top[i] then
            top.InsertBefore(num, i)
            if top.Length > 100 then
                top.Remove(top.Length - 1)
            end if
            exit for
        else
            if i = top.Length - 1 and i < 100 then
                top.Add(num)
            end if
        end if
    next
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