Arrays

Foundation

- Fixed size once created An array of arrays — rows can differ in length (jagged).

Core Java · pkg1core/core8ArraysDemo.java · pkg1core · core8ArraysDemo.java

- Arrays are fixed-size, zero-indexed, and store one type. - `arr.length` is a field (not a method). - java.util.Arrays provides sort, binarySearch, fill,…

Data structures · pkg3datastructures/datastructures0DynamicArray.java · pkg3datastructures · datastructures0DynamicArray.java

Blind 75 · Array · pkg5leetcode/blind75/blind75_LC11ContainerWithMostWater.java · pkg5leetcode · blind75_LC11ContainerWithMostWater.java

Two pointers move shorter line inward. Time O(n), Space O(1)

Blind 75 · Array · pkg5leetcode/blind75/blind75_LC121BestTimeToBuyAndSellStock.java · pkg5leetcode · blind75_LC121BestTimeToBuyAndSellStock.java

Track min price seen; maximize profit at each day. Time O(n), Space O(1)

Blind 75 · Array · pkg5leetcode/blind75/blind75_LC152MaximumProductSubarray.java · pkg5leetcode · blind75_LC152MaximumProductSubarray.java

Track max and min product ending at each index (negatives flip). Time O(n), Space O(1)

Blind 75 · Array · pkg5leetcode/blind75/blind75_LC153FindMinimumInRotatedSortedArray.java · pkg5leetcode · blind75_LC153FindMinimumInRotatedSortedArray.java

Binary search on unsorted half. Time O(log n), Space O(1)

Blind 75 · Array · pkg5leetcode/blind75/blind75_LC15ThreeSum.java · pkg5leetcode · blind75_LC15ThreeSum.java

Sort, fix i, two-pointer scan for triplets summing to zero. Time O(n^2), Space O(1) excluding output

Blind 75 · Array · pkg5leetcode/blind75/blind75_LC1TwoSum.java · pkg5leetcode · blind75_LC1TwoSum.java

One-pass hash map stores value->index; check complement each step. Time O(n), Space O(n)

Blind 75 · Array · pkg5leetcode/blind75/blind75_LC217ContainsDuplicate.java · pkg5leetcode · blind75_LC217ContainsDuplicate.java

HashSet detects repeated values. Time O(n), Space O(n)

Blind 75 · Array · pkg5leetcode/blind75/blind75_LC238ProductOfArrayExceptSelf.java · pkg5leetcode · blind75_LC238ProductOfArrayExceptSelf.java

Prefix and suffix products without division. Time O(n), Space O(1) excluding output

Blind 75 · String · pkg5leetcode/blind75/blind75_LC242ValidAnagram.java · pkg5leetcode · blind75_LC242ValidAnagram.java

Frequency count arrays for both strings. Time O(n), Space O(26)

Blind 75 · DP · pkg5leetcode/blind75/blind75_LC300LongestIncreasingSubsequence.java · pkg5leetcode · blind75_LC300LongestIncreasingSubsequence.java

Patience sorting with binary search on tails array. Time O(n log n), Space O(n)

Blind 75 · Array · pkg5leetcode/blind75/blind75_LC33SearchInRotatedSortedArray.java · pkg5leetcode · blind75_LC33SearchInRotatedSortedArray.java

Binary search identifying sorted half. Time O(log n), Space O(1)

Blind 75 · Array · pkg5leetcode/blind75/blind75_LC53MaximumSubarray.java · pkg5leetcode · blind75_LC53MaximumSubarray.java

Kadane's algorithm tracks best ending-here sum. Time O(n), Space O(1)

Interview 150 · pkg5leetcode/interview150/interview150_LC167TwoSumII.java · pkg5leetcode · interview150_LC167TwoSumII.java

Sorted array two pointers from both ends. Time O(n), Space O(1)

Interview 150 · pkg5leetcode/interview150/interview150_LC189RotateArray.java · pkg5leetcode · interview150_LC189RotateArray.java

Reverse whole array then reverse first k and rest. Time O(n), Space O(1)

Interview 150 · pkg5leetcode/interview150/interview150_LC26RemoveDuplicates.java · pkg5leetcode · interview150_LC26RemoveDuplicates.java

Two pointers; write unique values at slow index. Time O(n), Space O(1)

Core Java — Interview Questions (200+)

Clear naming, small methods, immutability, proper exceptions, tests, and idiomatic APIs.

Collections Framework — Interview Questions (120+)

ArrayList = array (fast random access); LinkedList = nodes (fast head/tail ops).

Collections Framework — Interview Questions (120+)

Read-heavy, rarely-written shared lists.

Collections Framework — Interview Questions (120+)

By access pattern: order, uniqueness, sorting, concurrency.

Concurrency & Multithreading — Interview Questions (150+)

Prefer immutability and high-level concurrency utilities over low-level locks.

Functional Programming & Streams — Interview Questions (100+)

Keep lambdas pure, stateless, and non-interfering.

Generics — Interview Questions (60+)

Erasure makes array store checks unsound.

Generics — Interview Questions (60+)

Use bounded wildcards on input params (PECS), exact types on outputs.

Strings & Performance — Interview Questions (82+)

NPE if reference null on instance concat.

Java 9–21 Features — Interview Questions (95+)

infers raw-ish; specify generic.

Reflection & Annotations — Interview Questions (72+)

Panama native interop.

Effective Java & Best Practices — Interview Questions (82+)

Named constants.

Performance & Tuning — Interview Questions (60+)

Profile, fix the biggest bottleneck, verify, repeat.

Deterministic link

co-mentioned in interview title: ArrayList vs LinkedList perf?