Why is string concatenation in a loop O(n²)? How do you fix it? (StringBuilder)

Difficulty: 4/10

string concatenation, time complexity, StringBuilder

Efficient String Construction

Repeated concatenation of immutable strings inside a loop can become O(n²) because each concatenation may allocate a new string and copy the existing contents. As the accumulated string grows, the amount of copying grows as well.

javascript

1
Immutable strings cannot be modified in place.
2
Repeated concatenation may create many temporary objects.
3
The cumulative copying can become quadratic for a growing result.
4
StringBuilder maintains a mutable buffer and grows its capacity as needed.
5
With suitable capacity management, StringBuilder typically provides near-linear total construction time.

Scenario Questions

0-2 years experience

Follow-up Questions