Isomorphic Strings (LeetCode 205) | Full solution using a HashMap | Easy to understand

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Actual problem on LeetCode: leetcode.com/problems/isomorp...
Chapters:
00:00 - Intro
00:41 - Problem Statement and Description
03:37 - Brute Force has limitations
06:03 - Efficient Solution
09:39 - Dry-run of Code
13:01 - Final Thoughts
📚 Links to topics I talk about in the video:
LeetCode Problems: • Leetcode Solutions
Other String Problems: • Strings
Brute Force: • Brute Force algorithms...
📘 A text based explanation is available at: studyalgorithms.com
Code on Github: github.com/nikoo28/java-solut...
Test-cases on Github: github.com/nikoo28/java-solut...
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#leetcode #programming #interview

[@jaxsyntax]

Nikhil, you are one of the only people that make these problems simple and easy to understand. I appreciate your efforts very much!

[@rishabhjain7651]

exactly

[@user-lk6gr2je5j]

Thank you so much for making these problems simple and easy to understand, your explanation is best.

[@Maneeshce2007]

Really like the way of your explanation Nikhil , it encourages to solve DS problems which otherwise feels very frustrating.

[@hoddybhaba6704]

Great explaination!

[@dobermanbruce2397]

Really Appreciate your efforts

[@manishbhardwaj4587]

best teacher, its hard to follow others even if they have same solution as you!
Thankyou!!

[@vikashkatiyar1225]

u got a new subscriber ,
Thanks Nikhil for amazing quality content

[@adveshdarvekar7733]

If you are coding in c++, you will need 2 hashmaps as you can't make sure the letter is not present in the key as well as the value.

[@ashtonronald]

problem made extremely intuitive, gg!

[@lalanabiridi8358]

Hey nikhil i have a small doubt
what happenns if we dont create a new variable mapped char but instead directly compare original with replacement
i did that and out of 47 ..12 test cases failed

[@bahubali1939]

Amazing sirr!! We love you..........

[@acethoughtless1596]

Very nice explanation !! Thank you!!

[@nikoo28]

Glad it was helpful!

[@parthapardhu3319]

Wow.. simply good sir

[@BACSShaileshShettar]

great explanation

[@sohrab6494]

Your explanations are great and you make them so much easier to understand. Can you also solve '605. Can Place Flowers'?

[@nikoo28]

thank you so much...sure I will add it to my pipeline of upcoming videos.

[@vinayaksharma7134]

nice explanation

[@103_debopriyoghosh_cse_by6]

U are great , no idea why u are undeerrated

[@Harshu9669]

thanx brother

[@just_a_guy6985]

u dont need if condition at start in constraints its given that two strings are of same length

[@vilakshan.s]

As per leetcode looks like length of string can go till 5 * 10^4. So containsValue() can potentially end up doing nested looping with O(n) time complexity. Maybe we can improve this by having another reverse HashMap to improve the look up time. SpaceWise it will be 2X but I guess space is much cheaper than time :)

[@nikoo28]

Even if the string length is huge, you only have 256 different characters. This is almost constant time.

[@subee128]

Thanks

[@Isagi__000]

cool stuff.

[@hitheshpk6030]

Understood

[@mma-dost]

Java have a method to check the containsValue in the map, but cpp don't have that what should we do like creating another set for storing the values and then like check if the value contains in that something like this? This solved it but what about space complexity using map and set both.

[@nikoo28]

If you use std::unordered_map, which is implemented as a hash table, the average case time complexity for insertion, deletion, and search is O(1).

[@mma-dost]

thanks, bhaiya got it@@nikoo28

[@plutomessi21]

bhaiya this code passed 35/44 test cases
class Solution {
public boolean isIsomorphic(String s, String t) {
ArrayList s1 = new ArrayList();
ArrayList s2 = new ArrayList();
int count = 1;
for (int i = 1; i < s.length(); i++) {
if (s.charAt(i) == s.charAt(i - 1)) {
count++;
} else {
s1.add(count);
count = 1;
}
}
// s1.add(count);
int count1 = 1;
for (int i = 1; i < t.length(); i++) {
if (t.charAt(i) == t.charAt(i - 1)) {
count1++;
} else {
s2.add(count1);
count1 = 1;
}
}
s2.add(count1);
return s1.equals(s2);
}
}

[@nikoo28]

have a look at the code in the video description. You will find a github link. That code passes all cases :)

[@plutomessi21]

@@nikoo28 thank you bhaiya

[@mstinku9003]

easy way to solve this is l=len(set(zip(s,t)) a=len(s) b=len(t) return l==a==b: how easy it is using length

[@dobermanbruce2397]

😍😍😍😍😍😍😍😍😍😍😍

[@filmonghebremariam8981]

Are "afa" and "dde" Isomorphic or not?

[@nikoo28]

they are not

[@abhishekj2096]

This solution has runtime of 10ms and beats only 68%. Do you have a faster solution?

[@nikoo28]

don't go by these numbers you see on leetcode. If your solution is accepted, it is usually a good enough solution. The runtime usually depends on a lot of things:
- the startup time of the VM
- the language choice
- the processor of the VM
- the version of software stack

[@user-fq5wj3fj6d]

Will this code pass the test case
s = "12" t = "\u0067\u0068"

[@nikoo28]

did you try it out?

[@ArunKumar-gx8iv]

public boolean isIsomorphic(String s, String t) {
int n1 = s.length();
int n2 = t.length();
if (n1 != n2) {
return false;
}
HashMap mapST = new HashMap();
HashMap mapTS = new HashMap();
for (int i = 0; i < n1; i++) {
char c1 = s.charAt(i);
char c2 = t.charAt(i);
if (mapTS.containsKey(c1) && mapTS.get(c1) != c2) {
return false;
}
if (mapST.containsKey(c2) && mapST.get(c2) != c1) {
return false;
}
mapTS.put(c1, c2);
mapST.put(c2, c1);
}
return true;
}

[@delhidhamkhatushyam31]

how Paper and Title is isomorphic string you are teching wrong to students

[@Coder_421]

very bad video

[@nikoo28]

can you please let me know which part was difficult to understand?

[@Coder_421]

@@nikoo28 first description part it's self u confused

[@nikoo28]

which timestamp is confusing you? I added 4 different test cases to clear any confusion.

[@Coder_421]

@@nikoo28 paper title how e r l e can be mapped e is common 4 case also true

[@nikoo28]

@@Coder_421 if "paper" is your start string, you are mapping E -> L, and R -> E
but if "title" is your start string, then you map L -> E and E -> R
You are mapping different characters.
But in case 4, when you start from "kikp" you are mapping the same character K once to B and then to D. This is not allowed.

[@vivekkumaryadav9862]

def isIsomorphic(self, s, t):
map1 = []
map2 = []
for idx in s:
map1.append(s.index(idx))
for idx in t:
map2.append(t.index(idx))
if map1 == map2:
return True
return False

[@Krixnbhakt]

I'm not able to understand the second else condition - else{ char mappedCharacter = charMappingMap.get(original); if (mappedCharacter != replacement)return false;}

[@anilkumarsingh7141]

Just think opposite like s1 = "kikp" and s2 = "badc" . I hope you got it