java 25 lines · 6 steps

Merging two sorted arrays in Java

Two pointers walk both sorted inputs in lockstep, copying the smaller head each time to build one merged array in linear time.

Explained by highlit
Beginner two-pointers merging arrays linear-time
1public class SortedListMerger {
2 
3 public static int[] merge(int[] a, int[] b) {
4 int[] result = new int[a.length + b.length];
5 int i = 0, j = 0, k = 0;
6 
7 while (i < a.length && j < b.length) {
8 if (a[i] <= b[j]) {
9 result[k++] = a[i++];
10 } else {
11 result[k++] = b[j++];
12 }
13 }
14 
15 while (i < a.length) {
16 result[k++] = a[i++];
17 }
18 
19 while (j < b.length) {
20 result[k++] = b[j++];
21 }
22 
23 return result;
24 }
25}
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1When both inputs are already sorted, a single linear pass beats re-sorting the combined data.
  2. 2Independent pointers let you consume two sequences at different rates without nested loops.
  3. 3Always handle the leftover tail of whichever input outlasts the other after the main merge ends.

Related explainers

java 
public class ThumbnailProcessor {
 
    private static final int MAX_CONCURRENCY = 4;
 

Bounded parallel thumbnail rendering in Java

concurrency thread-pool futures
Intermediate 7 steps
java 
import java.util.ArrayDeque;
import java.util.Deque;
 
public final class RollingAverage {

A rolling average over a sliding window

sliding-window running-sum deque
Intermediate 7 steps
java 
@Target({ElementType.FIELD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = StrongPasswordValidator.class)
@Documented

Building a custom @StrongPassword validator in Spring

bean-validation annotations regex
Intermediate 7 steps
java 
@Component
public class JwtAuthenticationFilter extends OncePerRequestFilter {
 
    private final JwtTokenProvider tokenProvider;

How a JWT auth filter works in Spring

authentication jwt servlet-filter
Intermediate 8 steps
java 
@Entity
@Table(name = "accounts")
public class Account {
 

Optimistic locking with @Version in Spring

optimistic-locking jpa concurrency
Advanced 7 steps
java 
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.math.BigInteger;
 

A thread-safe memoized factorial cache

memoization thread-safety caching
Intermediate 6 steps

Share this explainer

Here's the card — post it anywhere.

Merging two sorted arrays in Java — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code