Swift - Collections
Given an empty Swift array
var items = [String](), which sequence of operations will result in ["Pen", "Book", "Eraser"]?Given an empty Swift array var items = [String](), which sequence of operations will result in ["Pen", "Book", "Eraser"]?
hard📝 Application Q15 of 15
Step-by-Step Solution
Solution:
Step 1: Start with empty array and insert "Pen" at index 0
items = ["Pen"]Step 2: Insert "Book" at index 1 and "Eraser" at index 2
items = ["Pen", "Book", "Eraser"]Step 3: Check other options for correctness
items.append("Pen")
items.insert("Book", at: 0)
items.append("Eraser"): append "Pen" -> ["Pen"]; insert "Book" at 0 -> ["Book", "Pen"]; append "Eraser" -> ["Book", "Pen", "Eraser"] (wrong order).
items.append("Pen")
items.append("Book")
items.insert("Eraser", at: 1): append "Pen", append "Book" -> ["Pen", "Book"]; insert "Eraser" at 1 -> ["Pen", "Eraser", "Book"] (wrong order).
items.insert("Pen", at: 1)
items.append("Book")
items.append("Eraser"): insert "Pen" at 1 on empty array -> index out of range error.Final Answer:
items.insert("Pen", at: 0)
items.insert("Book", at: 1)
items.insert("Eraser", at: 2) -> Option AQuick Check:
Insert at correct indexes builds array [OK]
Quick Trick: Insert at indexes 0,1,2 to build array step-by-step [OK]
Common Mistakes:
- Inserting at invalid index in empty array
- Confusing append and insert order
- Assuming insert can add beyond current size
Master "Collections" in Swift
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