# 分治法思想-找出第k小元

```python
'''
思路：拆成多个lower,pi,high划分。lower中的比pi小，high中的比pi大
'''
def partition(seq):
    '''
    序列转成左，中，右
    '''
    pi=seq[0]
    lower=[x for x in seq[1:] if x<=pi]
    high=[x for x in seq[1:] if x>pi]
    print(lower,pi,high)
    return lower,pi,high

def search(seq,k):
    lower,pi,high=partition(seq)
    m=len(lower)
    if m==k-1:
        return pi
    elif m<k-1:
        return search(high,k-1-m)
    else:
        return search(lower,k)

data=[4,1,6,3,7,9,13,93,0,100,2]
print(search(data,8))
print(sorted(data))
```

```
[1, 3, 0, 2] 4 [6, 7, 9, 13, 93, 100]
[] 6 [7, 9, 13, 93, 100]
[] 7 [9, 13, 93, 100]
[] 9 [13, 93, 100]
9
[0, 1, 2, 3, 4, 6, 7, 9, 13, 93, 100]
```


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