50 lines
1.3 KiB
Python
50 lines
1.3 KiB
Python
''' mbinary
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#########################################################################
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# File : select.py
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# Author: mbinary
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# Mail: zhuheqin1@gmail.com
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# Blog: https://mbinary.xyz
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# Github: https://github.com/mbinary
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# Created Time: 2018-07-06 17:13
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# Description:
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#########################################################################
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'''
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from random import randint
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def select(lst,i):
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lst = lst.copy()
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def partition(a,b):
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pivot = lst[a]
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while a<b:
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while a<b and lst[b]>pivot: b-=1
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if a<b:
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lst[a] = lst[b]
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a+=1
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while a<b and lst[a]<pivot: a+=1
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if a<b:
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lst[b] = lst[a]
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b-=1
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lst[a]= pivot
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return a
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def _select(a,b):
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if a>=b: return lst[a]
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# randomized select
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n = randint(a,b)
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lst[a],lst[n] = lst[n],lst[a]
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pos = partition(a,b)
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if pos>i:
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return _select(a,pos-1)
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elif pos<i:
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return _select(pos+1,b)
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else:return lst[pos]
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return _select(0,len(lst)-1)
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if __name__ =='__main__':
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lst = [randint(0,1000) for i in range(100)]
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st = sorted(lst)
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for i in range(10):
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n = randint(0,99)
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print('select {}th: \nexpect: {}\ngot: {}'.format(n,st[n],select(lst,n)))
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