Count Unique Characters of All Substrings of a Given String | Leetcode 828

This video explains a very important interview problem which is to Count Unique Characters of All Substrings of a Given String. This problem is a common Amazon, Microsoft interview problem. It is based on counting unique characters in all substrings of a string.
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[@anuragkhugshal7792]

After struggling for hours with text solutions, finally understood it from this beautiful explanation.

[@techdose4u]

Great :)

[@gauravsingla6444]

Same

[@akhilkumarp]

Very good and planned explanation., Understood in a shot

[@techdose4u]

Great ❤️

[@lapujain]

Your teaching style is awesome. Keep up the good work.

[@mdaasil2329]

Very well explained! Thanks TechDose.

[@RajiurRahman1]

Thank you, your explanation was very easy to understand. You made a difficult problem somewhat easy, at least "medium".

[@tien556]

This is a master piece thank you so much!

[@phantom3612]

idea is:
Find contribution of each char in string
eg. ABCABDA
here we see A at starting: putting A in middle
Check LHS size = 1 & RHS side (as long as A is unique) 4
Doing 1*4 = 4 (gives contribution of first A)
Similarlily, do rest all chars and add up at the end!
How do we know this? Observation & Dry run to check!
-----------------------------------------------
Approach---
Create a MAP (for constant time lookup) of vector of occurence
A-> 0-3-6
B-> 1-4
C-> 2
D-> 5
Now, do add -1 before each vec and n after each vec in map
So that when we check for each occurence (since we know index)
we can do e.g.[0], 0-(-1) * (3-0) = 1
and for [6], (6-3)* (n-6) = 3*1 = 3
and [3], (3-0)*(6-3) = 3*3 = 9
ADDING UP, 1+3+9 = 13

[@himaniupadhyay8201]

Best Explanation with intution

[@mrinalkumar9453]

Wonderful explanation❤

[@zz-oq2dt]

very smart!!!😀

[@priyadarshinir9730]

Very Good Explanation!
how's the time complexity O(N)?
we have a list of list and for each list we count.
isn't it a time complexity near to O(N^2)?

[@ash7130]

He is using the list of lists where the first list size is fixed to 26 alphabets, thus a constant. The only time required is to traverse the inner list whose worst case is 'len_of_string', i.e. O(n).

[@shashirajraja]

Nice Explanation!!

[@riteshsingh7067]

Is interview prep course still live?

[@techdose4u]

Yes

[@RahulKumar-be3lq]

@@techdose4u Congratulations, for AIR 1 in google kick-start round D

[@factswithabhi27]

@@techdose4u when the new batch get starting?

[@pironobcoding]

back after so long

[@techdose4u]

Yep :)

[@wilfredomartel7781]

👏👏

[@danielaviv8215]

what is the name of the software you are using?

[@hhcdghjjgsdrt235]

Avoid Flood In The City
please please please
explain this problem
why everyone is getting TLE ?
please please please

[@cunghocthuattoan7869]

Thank you so much! Very well explained!