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.

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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

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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.

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