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Closed
wants to merge 12 commits into from
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lazy_segment_tree.py-static-type-checking #2303

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aefe913
adding static type checking to basic_binary_tree.py
kanthuc Aug 8, 2020
e676647
Add static type checking to functions with None return type
kanthuc Aug 9, 2020
6310890
Applying code review comments
kanthuc Aug 10, 2020
0439180
Added missing import statement
kanthuc Aug 11, 2020
5005cbc
fix spaciing
kanthuc Aug 11, 2020
039cdb3
"cleaned up depth_of_tree"
kanthuc Aug 11, 2020
f1c86af
Add doctests and then streamline display() and is_full_binary_tree()
cclauss Aug 11, 2020
052f408
added static typing to lazy_segment_tree.py
kanthuc Aug 13, 2020
d5a446e
Merge branch 'master' of https://github.com/kanthuc/Python
kanthuc Aug 13, 2020
40371aa
pull from upstream repo
kanthuc Aug 13, 2020
8682782
added missing import statement
kanthuc Aug 18, 2020
15b1f62
modified variable names for left and right elements
kanthuc Aug 18, 2020
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65 changes: 37 additions & 28 deletions data_structures/binary_tree/lazy_segment_tree.py
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Original file line number Diff line number Diff line change
@@ -1,84 +1,93 @@
import math
from typing import List


class SegmentTree:
def __init__(self, N):
def __init__(self, N: int) -> None:
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Why is N in uppercase? Uppercase is reserved for constants in Python naming. Could we come up with a more self-documenting name than a single character?

self.N = N
self.st = [
self.st: List[int] = [
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What is st? Why does the reader have to guess? Can't we come up with a more self-documenting name?

0 for i in range(0, 4 * N)
] # approximate the overall size of segment tree with array N
self.lazy = [0 for i in range(0, 4 * N)] # create array to store lazy update
self.flag = [0 for i in range(0, 4 * N)] # flag for lazy update
self.lazy: List[int] = [
0 for i in range(0, 4 * N)
] # create array to store lazy update
self.flag: List[int] = [0 for i in range(0, 4 * N)] # flag for lazy update
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What exactly are we flagging with this variable? This type hint is not required. The typing system can already figure out that a list comprehension creates a list and that 0 is an int. This type hint just creates cognitive clutter for the reader.

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Sorry, the changes I made in this pr were already included in pr#2329 which was merged recently, so I closed this pr. I'll make these changes separately and send out a new pr. Thanks


def left(self, idx):
def left(self, idx: int) -> int:
return idx * 2

def right(self, idx):
def right(self, idx: int) -> int:
return idx * 2 + 1

def build(self, idx, l, r, A): # noqa: E741
if l == r: # noqa: E741
self.st[idx] = A[l - 1]
def build(
self, idx: int, left_element: int, right_element: int, A: List[int]
) -> None:
if left_element == right_element:
self.st[idx] = A[left_element - 1]
else:
mid = (l + r) // 2
self.build(self.left(idx), l, mid, A)
self.build(self.right(idx), mid + 1, r, A)
mid = (left_element + right_element) // 2
self.build(self.left(idx), left_element, mid, A)
self.build(self.right(idx), mid + 1, right_element, A)
self.st[idx] = max(self.st[self.left(idx)], self.st[self.right(idx)])

# update with O(lg N) (Normal segment tree without lazy update will take O(Nlg N)
# for each update)
def update(self, idx, l, r, a, b, val): # noqa: E741
def update(
self, idx: int, left_element: int, right_element: int, a: int, b: int, val: int
) -> bool:
"""
update(1, 1, N, a, b, v) for update val v to [a,b]
"""
if self.flag[idx] is True:
self.st[idx] = self.lazy[idx]
self.flag[idx] = False
if l != r: # noqa: E741
if left_element != right_element:
self.lazy[self.left(idx)] = self.lazy[idx]
self.lazy[self.right(idx)] = self.lazy[idx]
self.flag[self.left(idx)] = True
self.flag[self.right(idx)] = True

if r < a or l > b:
if right_element < a or left_element > b:
return True
if l >= a and r <= b: # noqa: E741
if left_element >= a and right_element <= b:
self.st[idx] = val
if l != r: # noqa: E741
if left_element != right_element:
self.lazy[self.left(idx)] = val
self.lazy[self.right(idx)] = val
self.flag[self.left(idx)] = True
self.flag[self.right(idx)] = True
return True
mid = (l + r) // 2
self.update(self.left(idx), l, mid, a, b, val)
self.update(self.right(idx), mid + 1, r, a, b, val)
mid = (left_element + right_element) // 2
self.update(self.left(idx), left_element, mid, a, b, val)
self.update(self.right(idx), mid + 1, right_element, a, b, val)
self.st[idx] = max(self.st[self.left(idx)], self.st[self.right(idx)])
return True

# query with O(lg N)
def query(self, idx, l, r, a, b): # noqa: E741
def query(
self, idx: int, left_element: int, right_element: int, a: int, b: int
) -> int:
"""
query(1, 1, N, a, b) for query max of [a,b]
"""
if self.flag[idx] is True:
self.st[idx] = self.lazy[idx]
self.flag[idx] = False
if l != r: # noqa: E741
if left_element != right_element:
self.lazy[self.left(idx)] = self.lazy[idx]
self.lazy[self.right(idx)] = self.lazy[idx]
self.flag[self.left(idx)] = True
self.flag[self.right(idx)] = True
if r < a or l > b:
if right_element < a or left_element > b:
return -math.inf
if l >= a and r <= b: # noqa: E741
if left_element >= a and right_element <= b:
return self.st[idx]
mid = (l + r) // 2
q1 = self.query(self.left(idx), l, mid, a, b)
q2 = self.query(self.right(idx), mid + 1, r, a, b)
mid = (left_element + right_element) // 2
q1 = self.query(self.left(idx), left_element, mid, a, b)
q2 = self.query(self.right(idx), mid + 1, right_element, a, b)
return max(q1, q2)

def showData(self):
def showData(self) -> None:
showList = []
for i in range(1, N + 1):
showList += [self.query(1, 1, self.N, i, i)]
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