Data Structures and algorithm are the most important part for cracking interview in any company.

There are multiple free resource available, I will list all of them on the basis of difficulty level.

Let's start .

1- Beginners

• Hackerrank
• Hackerearth
• GeeksforGeeks-Practice

(Best for basics)

2- Intermediate

• Leetcode
• InterviewBit
• Pepcoding

(Best for placement preparation)

3- Advance

• Codeforces
• Codechef
• Topcoder
• Atcoder

(Best for enhancing your coding skills)

If you want to add anything else then do comment it

Follow me for more such post.