What LeetCode problem types should freshers focus on for Java backend interviews?

For Java backend fresher interviews, I focus on the high-frequency patterns that show up repeatedly rather than trying to learn every algorithm. The core patterns I prioritize are arrays and strings using two-pointer or sliding window techniques, HashMap-based problems for frequency counting or lookups like Two Sum, basic tree traversals using BFS and DFS, and fundamental sorting and searching algorithms like binary search. I put most of my practice into Easy and Medium problems in these categories because they reinforce the fundamentals I need to explain clearly—companies want to see I can write clean, correct code under pressure for common scenarios, not that I've memorized some obscure Hard dynamic programming solution. Here's my strategy: I don't jump around randomly. Instead, I practise one pattern in a small batch, then mix it with older patterns to check that I can recognise it without a label. For example, I drilled two-pointer problems for a week straight—problems like Container With Most Water, trapping rainwater, and palindrome checking. After solving that many, I started recognizing the pattern signature: when I see a problem about finding pairs or subsequences in sorted data, I immediately think two pointers. I track which patterns I'm weak on in a spreadsheet and drill those specifically. The mistake I see other freshers make is jumping to Hard problems or dynamic programming too early because they want to feel advanced. Harder topics are more useful after the basic patterns are reliable; the target company's actual interview format should decide how far to go. I focus on depth over breadth—mastering a focused set of common patterns.