Big O describes how your code scales. It's the language of technical interviews.
Common complexities (fastest to slowest):
- : Constant. Hash table lookup (average case).
- : Logarithmic. Binary search.
- : Linear. Single loop through data.
- : Sorting algorithms.
- : Quadratic. Nested loops.
- : Exponential. Recursive without memoization.
What to say: "This solution is time and space because I loop once and use constant extra memory."
Career Changer Tip: Practice stating complexity for every solution you write. Make it automatic.