go 19 lines · 6 steps

Merging two sorted slices in Go

Two pointers walk two pre-sorted slices at once to produce a single sorted result in linear time.

Explained by highlit
Intermediate two-pointers merge slices algorithms
1func MergeSorted(a, b []int) []int {
2 merged := make([]int, 0, len(a)+len(b))
3 i, j := 0, 0
4 
5 for i < len(a) && j < len(b) {
6 if a[i] <= b[j] {
7 merged = append(merged, a[i])
8 i++
9 } else {
10 merged = append(merged, b[j])
11 j++
12 }
13 }
14 
15 merged = append(merged, a[i:]...)
16 merged = append(merged, b[j:]...)
17 
18 return merged
19}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1The merge step of merge sort runs in linear time because each element is visited exactly once.
  2. 2Pre-allocating a slice with a known capacity avoids repeated reallocation as it grows.
  3. 3After one input is exhausted, the remainder of the other is already sorted and can be appended wholesale.

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