DEV Community: ishwar kokkili

Day 2 - Valid Parentheses

ishwar kokkili — Tue, 24 May 2022 14:47:11 +0000

-> Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.

Eg ->

Input: s = "()"
Output: true

class Solution:
    def isValid(self, s: str) -> bool:
        stack =[]
        for i in s: 
            if i == "(" or i == "{" or i == "[" : 
                stack.append(i)
            elif i == ")" : 
                if stack and stack[-1]=="(": 
                     stack.pop()
                else: 
                    stack.append(i)
            elif i == "}" : 
                if stack and stack[-1]=="{": 
                    stack.pop()
                else: 
                    stack.append(i)
            elif i == "]" : 
                if stack and stack[-1]=="[": 
                    stack.pop()
                else: 
                    stack.append(i)

        if stack:
            return False 
        else: 
            return True

Recursion - Own Power function

ishwar kokkili — Fri, 20 May 2022 18:14:06 +0000

In this post I'm going to write my own power function in python which will perform like pow(x,n) in Py3

# Power function using recursion -> 

def power(num,exp):
    if exp==1: 
        return num 
    return num*power(num,exp-1)

print(f"The value is {power(5,3)})

output - The value is 125

Python - Leetcode : Day 1

ishwar kokkili — Fri, 20 May 2022 17:43:28 +0000

leetcode -> 344 -reverse string

344 - Reverse string -

Write a function that reverses a string. The input string is given as an array of characters s.

You must do this by modifying the input array in-place with O(1) extra memory

sol 1 - Pattern 'Stack' - Using a stack DS , but it uses O(N) extra memory.

sol 2 - 2 Pointer Approach - Using Two Pointers there is no need of Extra Memory
time complexity -O(N)
space complexity -O(1)

Code -

class Solution:   
    def reverseString(self, s: List[str]) -> None:
        """
        Do not return anything, modify s in-place instead.
        """
        i,j =0,len(s)-1
        while i<j : 
            s[i],s[j]=s[j],s[i]
            i+=1 
            j-=1
        return s