#!/usr/bin/env python3
from partition import partition
from random import randrange

def select(A,p,q,i):
    n = q - p + 1;  bad = True
    if n==1: return A[p]
    count = 0
    while bad:
        count+=1
        print(f"partition trial {count}")
        r = partition(A,p,q,randrange(p,q))
        k = r - p 
        if (k == i): return A[r]
        bad = (k< n//4) or (k> 3*n//4)
    if (i < k):
        return select(A,p,r-1,i)
    else:
        return select(A,r+1,q,i-k-1)

if __name__ == "__main__":
    from random import choices

    n=11

    A = choices(range(0,100),k=n)
    print("A=",A);

    median = select(A,0,n-1,n//2)
    print("median=",median)

    B=sorted(A)
    print("median via sorting = ",B[n//2])