javascriptadvanced10 minutes

Predict the Output of Complex Recursive Function with Memoization in JavaScript

Analyze a recursive JavaScript function that uses memoization and array transformations. Predict the output when the function is called with a specific argument.

Challenge prompt

Given the following JavaScript code which defines a recursive function that calculates a custom sequence with memoization and array transformations, predict the exact output of calling computeSequence(5). Explain your reasoning step-by-step.

Guidance

• Carefully trace the recursive calls and the memoization cache's population.
• Understand the use of array methods like map, reduce, and how they transform values at each recursion depth.

Hints

• Break down the function into smaller parts: focus first on the base case, then on the recursive case.
• Visualize or write down intermediate cache states after each call.

Starter code

function computeSequence(n, memo = {}) {
  if (n <= 1) return [n];
  if (memo[n]) return memo[n];

  const prev = computeSequence(n - 1, memo);
  const transformed = prev.map(x => x * n);
  const sum = transformed.reduce((acc, val) => acc + val, 0);

  memo[n] = [...prev, sum];
  return memo[n];
}

console.log(computeSequence(5));

Expected output

[0, 1, 3, 12, 60, 360]

Core concepts

recursionmemoizationarray transformationreduce method

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