DSA for placements: a 30-day plan for freshers

Days 1–7: Arrays and strings
Cover arrays, strings, hashing, two pointers and sliding window. Solve 2 Easy problems a day. Write the brute force first, then improve it.
```
Two Sum
Valid Anagram
Best Time to Buy and Sell Stock
Longest Substring Without Repeating Characters
```
Days 8–14: Recursion, sorting, binary search
Dry-run recursion on paper. Practise binary search on a sorted array and on the answer. If you can't solve a problem in 25 minutes, read the hint and re-solve it from scratch the next day.
```
Binary Search
Search in Rotated Sorted Array
Subsets
Merge Sorted Array
```
Days 15–21: Linked list, stack, trees
Cover linked list, stack, queue and binary trees with DFS and BFS. Explain your approach out loud while solving, as you would in an interview.
```
Reverse Linked List
Valid Parentheses
Maximum Depth of Binary Tree
Binary Tree Level Order Traversal
```
Days 22–27: Graphs and basic DP
Learn BFS and DFS on a grid, then 1D dynamic programming. Skip hard DP. Write the recurrence in one line before coding.
```
Number of Islands
Climbing Stairs
House Robber
Coin Change
```
Days 28–30: Timed mocks and apply
Do 3 timed mocks of 2 problems in 60 minutes with no hints, and revise your wrong ones. Start applying while you practise: open today's verified openings with official apply links.
```
hirastra.com/today
```

Skip the searching: today's verified openings are posted three times a day with official apply links, and you can check your resume against any of them with the free ATS checker.

Days 1–7: Arrays and strings

Days 8–14: Recursion, sorting, binary search

Days 15–21: Linked list, stack, trees

Days 22–27: Graphs and basic DP

Days 28–30: Timed mocks and apply