Speeding Up Calculations with Memoization (Caching)

In this lesson you will learn how to speed up calculations with memoization in C#, so the same work is not repeated. This is for anyone searching for "C# memoization how to use".

Memoization stores a result once it has been computed and returns it straight from storage the next time the same input arrives. Picture being asked the same question repeatedly and simply repeating the answer you remembered.

The sample code stores computed results in a Dictionary called cache, and each time SlowSquare() runs it checks cache.ContainsKey(n) to see whether the answer is already known. On the second call with the same input you see "Retrieved from cache" and the actual calculation is skipped.

A common stumbling block for beginners is judging when caching is worth it. Recursive calculations and API responses often show a noticeable speed-up, while lightweight work may not need it at all.

Spending memory to save computation time is the classic time/space trade-off, and a performance idea worth having in practice.

📖 Reference code

var cache = new Dictionary<int, int>();

int SlowSquare(int n) {
    if (cache.ContainsKey(n)) {
        Console.WriteLine($"Retrieved from cache: {n}");
        return cache[n];
    }
    Console.WriteLine($"Calculating: {n}");
    int result = n * n;
    cache[n] = result;
    return result;
}

Console.WriteLine(SlowSquare(5));
Console.WriteLine(SlowSquare(5));

✍️ Your code

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