Given two strings, s1 and s2, write code to check if s2 is a rotation of s1 using only one call to isSubstring().

checkSubstrRotation.ts

/*
  Assume you have a method called isSubstring() which checks if one word is a subtring of another.
  Given two strings, s1 and s2, write code to check if s2 is a rotation of s1 using only one call to
  isSubstring(). Eg "waterbottle is a rotation of erbottlewat"
*/
function checkSubstr(s1: string, s2: string): boolean {
  if (s1.length !== s2.length) {
    return false
  }
  const rotationByIndex = new Map()

  for (let i = 0; i < s2.length; ++i) {
    const char = s2[i]
    for (let rIndex = 0; rIndex <= i; ++rIndex) {
      if (rIndex === 0 && !rotationByIndex.get(i)) {
        rotationByIndex.set(i, [])
      }

      const rotation = rotationByIndex.get(rIndex)
      if (!rotation) {
        continue
      }
      if (char === 'a' && rIndex === 1) debugger
      if (char === s1[rotation.length]) {
        rotation.push(char)
      } else {
        rotationByIndex.delete(rIndex)
      }
    }
  }

  const keys = Array.from(rotationByIndex.keys())
  if (keys.length > 1) throw 'should never happen'
  if (keys.length === 0) return false

  const key = parseInt(keys[0])
  const firstSlice = s2.slice(0, key)
  const secondSlice = s2.slice(key, s2.length)

  return s1.includes(secondSlice.concat(firstSlice))
}