Evaluate Reverse Polish Notation | 2 Approaches | Leetcode 150

This is the 6th Video of our Playlist "Stack  : Popular Interview Problems".In this video we will try to solve two very good Stack based problem : Evaluate Reverse Polish Notation | 2 Approaches | Leetcode 150
I will explain the intuition so easily that you will never forget and start seeing this as cakewalk EASYYY.
We will do live coding after explanation and see if we are able to pass all the test cases. 
Also, please note that my Github solution link below contains both C++ as well as JAVA code.

Problem Name :  Evaluate Reverse Polish Notation | 2 Approaches | Leetcode 150
Company Tags  : will update soon

Approach Summary : The algorithm iterates through the input vector of strings representing RPN expressions, pushing operands onto the stack and performing operations when encountering operators. The final result is obtained by evaluating the entire expression, and the result is returned.You can also use map to store functions for different operators

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 Timelines
00:00 - Introduction
0:25 - Problem Explanation
4:17 - Dry Run Explanation
7:05 - Coding it up
11:26 - Using Unordered_map and Lambda
17:05 - Coding it up

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[rohankadam]

How the heck this video has less views? Btw amazing tutorial thank you.

[piyushacharya]

bohot sahi time pe video dale ho bhai.

[Ankitkumar-fzkc]

I already solved this question my own but just come here to learn your approach and i learnt something new thanks MIK.

[bhuppidhamii]

thank you, I learned how to write lambda function today!

[gauravbanerjee]

Thanks a lot bhaiya ❤❤ aaj 2nd method se kuch naya sikhne ko mila 😁

[oqant]

LEARNT A LOT FROM THIS QUESTION...A BIG THANKS TO U BHAIYA🙌

[Aimer]

what the hell yar, how less views on this video are?? it should be on top😍😍

[souravjoshi]

I forked your repo man. I am making notes from your Github repo. It's like a super resource

[Avi-wvnb]

Feeling so good that this channel is growing.

[oqant]

Learnt something new (lambda wala part)
Thanks❤❤

[saumypandey]

Bro...The way you speak is very soothing to learn...thank you!!
Watching your graph playlist nowadays

[manishv.]

Always Get something new with your video .

[wearevacationuncoverers]

JAVA version for Lambda approach :
class Solution {
public int evalRPN(String[] tokens) {
Stack<Integer> st = new Stack<>();
int result = 0;

Map<String, BiFunction<Integer, Integer, Integer>> mp = new HashMap<>();
mp.put("+", (a, b) -> a + b);
mp.put("-", (a, b) -> a - b);
mp.put("*", (a, b) -> (int)((long)a * (long)b));
mp.put("/", (a, b) -> a / b);

for (String s : tokens) {
if (mp.containsKey(s)) {
int b = st.pop();
int a = st.pop();

result = mp.get(s).apply(a, b);
st.push(result);
} else {
st.push(Integer.parseInt(s));
}
}
return st.pop();
}
}

[Manash_B]

Thanks Sir! got to learn a new thing today.

[satyaprakashtiwari]

i did this question, but still came to your video to see how you have done, and again you did great

[ujjawalraj]

Learned how to write lambda for map and how to creatr a map of key, function nice

[pranjalyadav]

interesting tutorial broo!!
specially writing lamda

[oqant]

/*note lets say 8/4 hence 8 will come first in stack
and 4 will later hence hence 4 will be on top of stack lets say it is b and then 8 will be below 4 in stack lets say it is a hence
in operation we will pass(8, 4, "/")
so that it will calculate as 8/4
hence we pass a, b not as b, a
*/
order of sending a and b will matter a lot
hope it might be helpful for someone

[YashSinghal]

Postfix Expressions. DS classes in BTech :)

[abc-ymzs]

i have one doubt we are converting those values to long but when we are returning we should store them in long long but we are storing why we are not getting integer over flow