Segment tree min and max

Question

I am trying to build a segment tree whose parent node should contain min and max values of its children nodes.Now when I am trying to implement this I am facing an error which is that one child can return an integer whereas other child can return a list and operating max or min function will raise an error.How to overcome this?

from math import log2,ceil
def segment(low,high,pos):

    if (low==high):
        segment_tree[pos]=arr[low]
        return

    mid=(high+low)//2

    segment(low,mid,2*pos+1)
    segment(mid+1,high,2*pos+2)

    segment_tree[pos]=[min(segment_tree[2*pos+1],segment_tree[2*pos+2]),max(segment_tree[2*pos+1],segment_tree[2*pos+2])]

length=5
arr=[1,2,3,4,5]
low=0
high=length-1
height=int(ceil(log2(length)))
pos=0 
size_of_segment_tree=2*int(pow(2,height))-1
segment_tree=[0]*size_of_segment_tree
segment(low,high,pos)

may be you should add this logic somewhere: `sum(your_object) if instance(your_obj, list) else your_object` — Moinuddin Quadri, Jan 07 '18 at 12:25
The code, as it is formatted, will give error since segment_tree is a global function that needs to be defined so in the function. — rnso, Jan 07 '18 at 12:41
See this: https://docs.python.org/3/faq/programming.html#what-are-the-rules-for-local-and-global-variables-in-python — rnso, Jan 07 '18 at 13:01

score 1 · Accepted Answer · edited Jan 07 '18 at 14:13

This will work using isinstance(object, list)

segment_tree[pos]=[min(min(segment_tree[2*pos+1]) if isinstance(segment_tree[2*pos+1],list) else segment_tree[2*pos+1],min(segment_tree[2*pos+2]) if isinstance(segment_tree[2*pos+2],list) else segment_tree[2*pos+2]),max(max(segment_tree[2*pos+1]) if isinstance(segment_tree[2*pos+1],list) else segment_tree[2*pos+1],max(segment_tree[2*pos+2]) if isinstance(segment_tree[2*pos+2],list) else segment_tree[2*pos+2])]

Edit: reformatting for clarity:

segment_tree[pos]=  [
    min(min(segment_tree[2*pos+1]) 
        if isinstance(segment_tree[2*pos+1],list) 
        else segment_tree[2*pos+1],
    min(segment_tree[2*pos+2]) 
        if isinstance(segment_tree[2*pos+2],list) 
        else segment_tree[2*pos+2]),
    max(max(segment_tree[2*pos+1]) 
        if isinstance(segment_tree[2*pos+1],list) 
        else segment_tree[2*pos+1],
    max(segment_tree[2*pos+2]) 
        if isinstance(segment_tree[2*pos+2],list) 
        else segment_tree[2*pos+2])
        ]

I have added a reformatted version to clarify this excellent code. — rnso, Jan 07 '18 at 14:14

score 0 · Answer 2 · answered Jan 07 '18 at 12:38

You could write a min/max function yourself if I understood the problem right:

def my_min(value):
    if isinstance(value, list):
        return min(value)
    else:
        return value

def my_max(value):
    if isinstance(value, list):
        return max(list)
    else:
        return value

Segment tree min and max

2 Answers2