Java Algorithms

Two examples of character mapping. On the left, abbcdd over qwwcrr, with the pairs a and q, b and w, c and c, d and r, so the strings are isomorphic. On the right, aab over que, where a pairs with q at index 0 and with u at index 1, so the strings are not isomorphic.

Isomorphic Strings in Java: Algorithm, Code and Examples

Two strings are isomorphic when a one-to-one character mapping turns one into the other. Learn the algorithm and check it in Java with arrays or two HashMaps.

Big O Notation: Measuring the Algorithm Efficiency

Big O notation categorizes the efficiency of a given algorithm and describes the upper bound of the growth rate of a function as the input grows.

Recursion in Java: Base Case, Call Stack and Examples

Learn recursion in Java with call stack diagrams, base cases, factorial and Fibonacci examples, memoization and how to avoid StackOverflowError.

Java EdDSA Example: Sign and Verify With Ed25519 and Ed448

Java EdDSA example with Ed25519 and Ed448. Generate keys, sign and verify messages, save and load keys, and compare EdDSA with ECDSA, RSA and ML-DSA.

Quicksort in Java: Algorithm, Code and Performance

Learn quicksort in Java with a partition diagram, Lomuto and Hoare code, pivot choice, worst-case fixes and a comparison with Arrays.sort() on Java 25.

Bubble Sort in Java: Algorithm, Code and Performance

Learn bubble sort in Java with a pass-by-pass diagram, the basic and optimized code, sorting objects, and timings against selection and insertion sort.

Selection Sort in Java: Algorithm, Code and Performance

Learn selection sort in Java with a step diagram, code for arrays and objects, why it is not stable, and how it compares with other simple sorts.

Insertion Sort in Java: Algorithm, Code and Performance

Learn insertion sort in Java with a step diagram, shifting and binary insertion code, and why it beats Arrays.sort() on small or nearly sorted arrays.

Merge Sort in Java: Algorithm, Code and Performance

Learn merge sort in Java with a split and merge diagram, top-down and bottom-up code, stability, memory use and a comparison with TimSort on Java 25.

Soundex Algorithm in Java: Phonetic Search Examples

Implement the Soundex algorithm in Java, use Apache Commons Codec, handle the H and W rule, and compare Soundex with Metaphone and edit distance.

Java Compare and Swap (CAS): How It Works With Examples

Compare and swap (CAS) writes a new value only if a variable still holds the value we read. Learn compareAndSet(), CAS loops, VarHandle and the ABA problem in Java 25.