What is the difference between memoization and tabulation?

They are two directions through the same state graph. Memoization starts at the requested state and recurses into dependencies, storing answers on the way back. Tabulation starts at the base states and computes forward until the target state is ready.

function fibMemo(n, memo = new Map()) {
  if (n <= 1) return n;
  if (memo.has(n)) return memo.get(n);
  const value = fibMemo(n - 1, memo) + fibMemo(n - 2, memo);
  memo.set(n, value);
  return value;
}

function fibTab(n) {
  if (n <= 1) return n;
  let prev = 0;
  let current = 1;
  for (let i = 2; i <= n; i++) {
    const next = prev + current;
    prev = current;
    current = next;
  }
  return current;
}

Choosing between them

• Memoization follows the recurrence directly and is easy to reason about
• Tabulation avoids recursion limits and often has better constants
• Memoization may skip states that the target never needs
• Tabulation may compute states that are not required
• Some state graphs are easier to express top-down, especially with pruning

Space can often be reduced in the tabulated version. If each state depends only on the previous row or the previous two values, keep rolling variables instead of the full table. The same reduction is harder to see in the recursive version.