How do you check if a Dictionary contains a specific key or value?

Short answer: ContainsKey(key) – checks for key existence ContainsValue(value) – checks for value Example: dictionary.ContainsKey("Alice"); // true/false dictionary.ContainsValue(30); // true/false

Example code

ContainsKey(key) – checks for key existence ContainsValue(value) – checks for value Example: dictionary.ContainsKey("Alice"); // true/false
dictionary.ContainsValue(30); // true/false

Real-world example (ShopNest)

ShopNest caches product prices in a Dictionary<string, decimal> keyed by SKU so checkout can look up a price in O(1) instead of scanning a list.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.