LeetCode 224,227,772 Basic Calculator 1,2,3 Explanation and Solution

LeetCode 224 Basic Calculator
LeetCode 227 Basic Calculator 2
LeetCode 772 Basic Calculator 3

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[AbhishekKumar-yvih]

Although it's a bit difficult to understand some of the words at first. But the Algorithm and illustration is so easy to understand as well as it's lucid and general. Glad to find this channel. Hub of hard leetcode.

[jinghuang]

This is genius! Happy girl makes me happy as well!

[aunnfriends]

Here is the converted Python code for 227 since this one has a special handling needed for the division:

class Solution:
def calculate(self, s: str) -> int:
from collections import deque
q = deque(list(filter(lambda x: x != ' ', s)))
q.append(' ')
def backtracking(q:deque)-> int:
pre, num, place_holder, pre_op = 0, 0, 0, '+'
while q:
ch = q.popleft()
if ch >= '0' and ch <= '9':
num = num * 10 + int(ch)
elif ch == '(':
# pass by reference
num = backtracking(q)
else:
if pre_op == '+':
place_holder += pre
pre = num
elif pre_op == '-':
place_holder += pre
pre = -num
elif pre_op == "*":
pre *= num
elif pre_op == "/":
tmp = pre // num

if tmp < 0 and pre % num != 0:
tmp += 1
pre = tmp


if ch == ")": break
pre_op = ch
num = 0
return pre + place_holder

return backtracking(q)

[umabharati]

It took a couple of attempts for me to understand this code, but this is a wonderful solution! keep it up.

[reyazbasha]

Very helpful and your notes makes it easy to understand. Thank you !!

[adarshjadhav]

Really appreciate your hard work.. especially speaking English without being native speaker

[suhasnayak]

Thank you for the solution :-)
If you loop over String s and remove one character at a time, you will save that extra space used for queue. How much space is used by the DFS recursion call ? What is the time and space complexity ?

[reshmadokania]

What is the time complexity for this ?

[psn]

thanks a lot. This question is asked by Uber

[MrUnemployedYouth]

I'm glad that you are doing this. Very helpful!

[amitashah]

So if input is only number, for example 335, solution breaks?

[raghurambhagawatula]

isn't there a Stack based solution for this, as interviewers might perfer iterative approach

[gollapudibhargav]

Great video overall. I felt that some parts (eg. tracing with example) could have been more clear, nevertheless, it's a great video!

[siobhanahbois]

Sorry if this is stupid (and I blame NYE celebrations) but why do we need to remove whitespace?

[suhasnayak]

Can you also please explain how to handle negative integer values.