Select2

O(n)

Divide n elements into groups of 5 elements and one group of (n mod 5) elements

O(n)

Find median of each group.

T($\lceil$(n/5)$\rceil$)

Use Select2 recursively to find median of medians

O(n)

Partition n elements around median into k and n-k elements.

T(7n/10 + 6)

If i $\leq$ k
then use Select2 to find ith element in k lower elements
else use Select2 to find (i-k)th element in n-k higher elements

Example

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