Find longest common substring (Memoization)

Given two strings 's1' and 's2', find the length of the longest common substring.

Hint

This algorithm uses memoization to improve performance. It's same as the recursive version of Find longest common substring, but with a special 'cache' to store results. The 'cache key' is crucial. It's how we identify and store past results. Sometimes we need one key, sometimes multiple keys. We add code to:

• Initialize cache to store results.
• Using the key to check cached result. If the result is not found in the cache, do the calculation and save the result in cache.
• Return the cached result.

• Python
• Javascript
•  Run

cache = {}

def count(s1, s2):
  if s2 == "":
    return 0
  
  global cache
  if s2 not in cache:

    if s2 in s1:
      cache[s2] = len(s2)
    else:
      cache[s2] = max(count(s1, s2[1:]), count(s1, s2[:-1]))

  return cache[s2]

s1 = "QuestionOfTheDay"
s2 = "NewQuestion"

print(count(s1, s2))

const cache = {}

function count(s1, s2) {
  if (s2 === "") {
    return 0;
  }

  if (cache[s2] === undefined) {
    if (s1.indexOf(s2) >= 0) {
      cache[s2] = s2.length;
    } else {
      cache[s2] = Math.max(count(s1, s2.slice(1)), count(s1, s2.slice(0, -1)));
    }
  }

  return cache[s2];
}

const s1 = "QuestionOfTheDay";
const s2 = "NewQuestion";

console.log(count(s1, s2));