Amortized Cost — Why ArrayList.add() is O(1) #computer-science #O(1) #big-o #arraylist

Added: 2026-05-07

[00:00:00]Adding to a dynamic array takes O1 until the array fills up. Then it doubles and copies every element. That single operation costs O and N. So, is add O1 or ON? The resize at size N follows resizes at 1, 2, 4, 8, and so on. Total work across all N insertions, 2N - 1.

[00:00:19]Divide by N, average cost per insertion, O1. Amortized cost measures what you pay on average, not what you pay once.