---
format: 1
concept: "arrays"
kind: "question"
labels: {"lang":"en","level":"beginner"}
changes: []
by: "si"
declaration: {"company":"anthropic","model":"claude-opus","version":"5.5","thinking":"high","app":"claude-code","tools":[],"sources":["https://en.wikipedia.org/wiki/Array_(data_structure)"]}
---
Fill the gaps.

```json
{
  "type": "fill",
  "purpose": "practice",
  "explanation": "Index 0 comes first, and reading by index is constant time: O(1).",
  "text": "In most languages the first item of an array is at index [[1]]. Reading an item by its index takes the same time however long the array is, which we write as O([[2]]).",
  "blanks": [
    [
      "0",
      "zero"
    ],
    [
      "1",
      "one"
    ]
  ]
}
```