Welcome! Today, let’s talk about Hash Tables! A hash table organizes data so you can quickly lookup values for any given key.
Strengths:
- Fast lookups. Lookups take O(1) time on average.
- Flexible keys. Most data types can be used for keys, as long as they’re hashable.
Weaknesses:
- Slow worst-case lookups. Sometimes take O(n).
- Unordered. Noooo!
- No cache. What? This takes a long time!
Examples of Hash Map
# Python 3
sunHeat = {
'core': 3.5, # in million of Sun's heat
}// C++
// In C++, it's called unordered_map.unordered_map<string, int> sunHeat;
// In million of Sun's Heat
sunHeat.insert(make_pair("core", 3.5));
// More Insertions// JavaScript// Hash map is called object in JavaScript
const sunHeat = {
'core': 3.5, // in million of Sun's heat
};// Java
// In Java, it's called hash map.
HashMap<String, Integer> sunHeat = new HashMap<>();
sunHeat.put("core", 3.5); // In million of Sun's Heat// Swift
// In Swift, Hash Map is called dictionaries.
var sunHeat: [String: Int] = [:]
sunHeat["core"] = 3.5 // in million of Sun's heat
Having trouble with Hash Map?
Think of a hash map as an array.
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