30 days of code

conditional : https://prepinsta.com/tcs-coding-questions/oxygen-level/

                       https://prepinsta.com/tcs-coding-questions/property-painting-coding-question/

                      https://www.includehelp.com/icp/101-pattern-count.aspx 

loop : https://practice.geeksforgeeks.org/problems/find-triplets-with-zero-sum/1

          If 5 digit number is input through keyboard, then WAP to print a new number by adding one                  to each digit. For ex. If the input is 12391 then output should be 23402.

           https://practice.geeksforgeeks.org/problems/armstrong-numbers2727/1

string : https://leetcode.com/problems/find-common-characters/

              https://leetcode.com/problems/reverse-string-ii/

array : https://www.codechef.com/problems/ALTARAY

            https://practice.geeksforgeeks.org/problems/longest-consecutive-subsequence2449/1

            Rotate array by n digits .

            Missing number in the array .

Dictionary / Map : https://www.hackerrank.com/challenges/ctci-ransom-note/problem?h_l=interview&playlist_slugs%5B%5D=interview-preparation-kit&playlist_slugs%5B%5D=dictionaries-hashmaps

                                https://www.hackerrank.com/challenges/frequency-queries/problem?h_l=interview&playlist_slugs%5B%5D=interview-preparation-kit&playlist_slugs%5B%5D=dictionaries-hashmaps

pattern : https://www.hackerrank.com/challenges/printing-pattern-2/problem

Recurssion : Write a function that returns all permutations of a given list. 

binary number : https://practice.geeksforgeeks.org/problems/is-binary-number-multiple-of-30654/1

2d array : https://hackerrank-challenge-pdfs.s3.amazonaws.com/17164-30-2d-arrays-English?AWSAccessKeyId=AKIAR6O7GJNX5DNFO3PV&Expires=1631379387&Signature=Gg0ML4eCe4bPWhIExB%2BrBY7FilU%3D&response-content-disposition=inline%3B%20filename%3D30-2d-arrays-English.pdf&response-content-type=application%2Fpdf

stack : https://practice.geeksforgeeks.org/problems/the-celebrity-problem/1

            https://practice.geeksforgeeks.org/problems/longest-valid-parentheses5657/1/

queue : https://practice.geeksforgeeks.org/problems/maximum-of-all-subarrays-of-size-k3101/1

linked list : https://leetcode.com/problems/palindrome-linked-list/

sorting : https://www.java67.com/2018/05/top-75-programming-interview-questions-            answers.html#ixzz76MGkjBDJ

                https://practice.geeksforgeeks.org/problems/relative-sorting4323/1

searching 1 : https://www.interviewbit.com/problems/search-for-a-range

searching 2 :

Problem Statement

Alex works at a clothing store. There is a large pile of socks that must be paired by color for sale. Given an array of integers representing the color of each sock, determine how many pairs of socks with matching colors there are.

For example, there are n=7 socks with colors ar = {1,2,1,2,1,3,2}. There is one pair of color 1 and one of color 2. There are three odd socks left, one of each color. The number of pairs is 2.

Function Description
Complete the sockMerchant function in the editor below. It must return an integer representing the number of matching pairs of socks that are available.
sockMerchant has the following parameter(s):
             n: the number of socks in the pile
             ar: the colors of each sock

Input Format
            The first line contains an integer n, the number of socks represented in ar.
            The second line contains n space-separated integers describing the colors ar[i] of the socks in the pile.

Constraints
             1 <= n <= 100
             1 <= ar[i] <= 100 & 0 <= i < n

Output Format
             Return the total number of matching pairs of socks that Alex can sell.

Sample Input
             9
             10 20 20 10 10 30 50 10 20
Sample Output
             3

Explanation

             Alex can match 3 pairs of socks i.e 10-10, 10-10, 20-20
             while the left out socks are 50, 60, 20

binary tree : https://leetcode.com/problems/trim-a-binary-search-tree/

                      https://leetcode.com/problems/invert-binary-tree/

                      https://leetcode.com/problems/subtree-of-another-tree/

Bitwise And : https://www.hackerrank.com/challenges/30-bitwise-and/problem