Evaluate Reverse Polish Notation | Python

Problem Statement:
Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are +, -, *, /. Each operand may be an integer or another expression.

Note:

The division between two integers should truncate toward zero.
The given RPN expression is always valid. That means the expression would always evaluate to a result and there won't be any divide by zero operation.
Example 1:

Input: ["2", "1", "+", "3", "*"]
Output: 9
Explanation: ((2 + 1) * 3) = 9
Example 2:

Input: ["4", "13", "5", "/", "+"]
Output: 6
Explanation: (4 + (13 / 5)) = 6
Example 3:

Input: ["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"]
Output: 22
Explanation:
  ((10 * (6 / ((9 + 3) * -11))) + 17) + 5
= ((10 * (6 / (12 * -11))) + 17) + 5
= ((10 * (6 / -132)) + 17) + 5
= ((10 * 0) + 17) + 5
= (0 + 17) + 5
= 17 + 5
= 22

Python for beginners: https://www.youtube.com/watch?v=egq7Z...

Code:
class Solution:
    def evalRPN(self, tokens: List[str]) -> int:
        l=[];
        for i in tokens:
            if(i=='+' or i=='-' or i=='*' or i=='/'):
                a=l.pop(-1);
                b=l.pop(-1);
                g=b+i+a;
                w=eval(g);
                e=int(w);
                l.append(str(e));
            else:
                l.append(i);
        return int(l[0]);

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if – if else – if else if ladder in C#

C#  IF Statement :

Syntax :

if(condition)
{
//code to be executed
}

Prog : Write a program to test whether a number is even or not

C#  IF-ELSE Statement :

Syntax :

if(Condition)
{
// code to be executed
}else
{
//Code if condition is false
}

Prog : Write a program to test whether a number is even or not

C# IF - ELSE - IF LADDER Statement :

Syntax :

if(Condition1)
{
//code to be executed
}else if (Condition2)
{
//code to be executed
}
else 
{
//Code when all the condition are false
}


Program : Write a program to print Grade of Student as per Marks.

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Mathematical functions | Python

For more detail on math module , check the below link: https://docs.python.org/3/library/mat... Relationship between number of digits of a number and it's logarithm: https://math.stackexchange.com/questi... Python for beginners: https://www.youtube.com/watch?v=egq7Z...

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Plus One | Python

Python for beginners: https://www.youtube.com/watch?v=egq7Z...

Code:

class Solution:

    def plusOne(self, digits: List[int]) -> List[int]:

        g="";

        for i in digits:

            g+=str(i);

        e=int(g);

        e=e+1;

        g=str(e);

        w=list(g);

        output=[];

        for i in w:

            output.append(int(i));

        return output;

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Majority Element | Python

Check the problem statement here:
https://leetcode.com/problems/majorit... Python for beginners: https://www.youtube.com/watch?v=egq7Z...

Code:


class Solution:
    def majorityElement(self, nums: List[int]) -> int:
        nums.sort();
        return nums[len(nums)//2];

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Max Consecutive Ones | Python

Check the problem statement here: Max Consecutive Ones https://leetcode.com/problems/max-con... Python for beginners: https://www.youtube.com/watch?v=egq7Z...
Code: class Solution: def findMaxConsecutiveOnes(self, nums: List[int]) -> int: g=""; for i in nums: g=g+str(i); e=g.split('0'); max=0; for i in e: if(max<len(i)): max=len(i); return max;

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eval | Python

Explore more about eval here: https://docs.python.org/3/library/fun... https://towardsdatascience.com/python... To convert the string into a numerical value use the function eval(string ) Test the following : a=eval(input()); type(a) Give a as 16 & check whether eval is converting input to a proper numeric datatype or not. Give a as 16.32 & check whether eval is converting a to proper numeric datatype or not. Python for beginners: https://www.youtube.com/watch?v=egq7Z...

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The continue Statement | Python

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end parameter in print() | Python

Python for beginners: https://www.youtube.com/watch?v=egq7Z... Web 🌐http://www.clcoding.com/ Telegram: https://t.me/clcoding_python https://www.facebook.com/pirawenpython/ https://www.facebook.com/groups/piraw...

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Handling Exceptions | Python

You can catch an exception by implementing the try—except construct. This construct is broken into 2 major parts: • try block. The try block indicates the code which is to be monitored for the exceptions listed in the except expressions. • except clause. You can use an optional except clause to indicate what to do when certain classes of exception/error occur (e.g. resolve the problem or generate a warning message). There can be any number of except clauses in sequence checking for different types of error/exceptions. For more detail explanation , check this below link: https://docs.python.org/3/tutorial/er... Python for beginners: https://www.youtube.com/watch?v=egq7Z...

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Mathematical Operations on Set | Python

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Nth term of GP | Python

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Is Subsequence | Python

Prerequisite: String in Python | Part 2.3 | Castor Classes https://www.youtube.com/watch?v=65z1V... Check the problem statement here: https://leetcode.com/problems/is-subs... Python for beginners: https://www.youtube.com/watch?v=egq7Z...

Code:


class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        g=0;
        for i in s:
            if(i in t):
                rs=t.index(i);
                t=t[rs+1:];
            else:
                g+=1;
        if(g==0):
            return True;
        else:
            return False;

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Set | Python

Python for beginners: https://www.youtube.com/watch?v=egq7Z... Web 🌐http://www.clcoding.com/ Telegram: https://t.me/clcoding_python https://www.facebook.com/pirawenpython/ https://www.facebook.com/groups/piraw...

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help & tab completion | Python

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what are the difference between LIST , TUPLE and SET in python ?

The tuple, list, set, dictionary are trying to solve the most important problems in programming, called, storage of data and retrieval of stored data in a way that is both easy to use, to code and to read for the programmers.
The big problems are:
- space availability
- insertion
- searching by value or position
- updating
- make the operations faster for big/huge data sets
Tuple:
When you only store data that you aren't changing and don't need to do search by value as you know the position.
List:
When you store data that you changing, inserting if fast and don't need to do search/update by value as you know the position
Set:
When you store data that changes from times to time, but most importantly you need very fast search by value as you don't know position then you use sets.The search is very fast as the set is indexed in memory and fast binary search used. Inserting and deletion is slow.
Dictionary:
When you need fast search, data doesn't change often, few updates and inserts. Is just advanced set where you store a group of key and value and search by the key.

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Largest Number At Least Twice of Others | Python

Python for beginners: https://www.youtube.com/watch?v=egq7Z...

Code:

class Solution:

    def dominantIndex(self, nums: List[int]) -> int:

        f=max(nums);

        rs=nums.index(f);

        u=[];

        g=0;

        for i in nums:

            if(i!=f):

                u.append(i);

        if(len(u)!=0):

            g=max(u);

        if(f>=2*g):

            return rs;

        else:

            return -1;

Telegram: https://t.me/clcoding_python 
https://www.facebook.com/pirawenpython/ 
https://www.facebook.com/groups/piraw...

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Ransom Note | Python

Python for beginners: https://www.youtube.com/watch?v=egq7Z...

Code:


class Solution:
    def canConstruct(self, ransomNote: str, magazine: str) -> bool:
        g=0;
        for i in ransomNote:
            t=ransomNote.count(i);
            s=magazine.count(i);
            if(t>s):
                g+=1;
        if(g==0):
            return True;
        else:
            return False;


Telegram: https://t.me/clcoding_python 
https://www.facebook.com/pirawenpython/ 
https://www.facebook.com/groups/piraw...

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Search Insert Position | Python

Python for beginners: https://www.youtube.com/watch?v=egq7Z...

Code:

class Solution:

    def searchInsert(self, nums: List[int], target: int) -> int:

        if(target in nums):

            return nums.index(target);

        else:

            if(target<min(nums)):

                return 0;

            elif(target>max(nums)):

                return len(nums);

            else:

                g=0;

                m=0;

                while(g<len(nums)):

                    if(nums[g]>target):

                        m=g;

                        break;

                    g=g+1;

                return m;

Telegram: https://t.me/clcoding_python 
https://www.facebook.com/pirawenpython/ 
https://www.facebook.com/groups/piraw...

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Intersection of Two Arrays | Python

Check the problem statement here: The intersection of Two Arrays: https://leetcode.com/problems/interse... Python for beginners: https://www.youtube.com/watch?v=egq7Z...

Code:


class Solution:
    def intersection(self, nums1: List[int], nums2: List[int]) -> List[int]:
        output=[];
        for i in nums1:
            if(i in nums2 and i not in output):
                output.append(i);
        return output;


Telegram: https://t.me/clcoding_python 
https://www.facebook.com/pirawenpython/ 
https://www.facebook.com/groups/piraw...

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Jewels and Stones | Python

Prerequisites for solving this particular question: String Immutability & count method | Python | Castor Classes https://www.youtube.com/watch?v=Am1vX... Iterate over a list & string | List in Python | Part 4 | Castor Classes https://www.youtube.com/watch?v=4Zrfk... You can get the problem statement here: https://leetcode.com/problems/jewels-... Python for beginners: https://www.youtube.com/watch?v=egq7Z...

Code:

class Solution:

    def numJewelsInStones(self, J: str, S: str) -> int:

        c=0;

        for i in J:

            c+=S.count(i);

        return c;

Telegram: https://t.me/clcoding_python 
https://www.facebook.com/pirawenpython/ 
https://www.facebook.com/groups/piraw...

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