Find Smallest Letter Greater Than Target

Description

Given a list of sorted characters letters containing only lowercase letters, and given a target letter target, find the smallest element in the list that is larger than the given target.

Letters also wrap around. For example, if the target is target = 'z' and letters = ['a', 'b'], the answer is 'a'.

Examples:

Input:
letters = ["c", "f", "j"]
target = "a"
Output: "c"
Input:
letters = ["c", "f", "j"]
target = "c"
Output: "f"
Input:
letters = ["c", "f", "j"]
target = "d"
Output: "f"
Input:
letters = ["c", "f", "j"]
target = "g"
Output: "j"
Input:
letters = ["c", "f", "j"]
target = "j"
Output: "c"
Input:
letters = ["c", "f", "j"]
target = "k"
Output: "c"

Note:

1. letters has a length in range [2, 10000].
2. letters consists of lowercase letters, and contains at least 2 unique letters.
3. target is a lowercase letter.

Solution(javascript)

/**
 * @param {character[]} letters
 * @param {character} target
 * @return {character}
 */
const nextGreatestLetter = (letters, target) => {
  const aux = (low, high, current) => {
    if (low > high) {
      return current
    }
    const middle = Math.floor((low + high) / 2)
    if (letters[middle] > target) {
      return aux(low, middle - 1, letters[middle])
    }
    return aux(middle + 1, high, current)
  }
  return aux(0, letters.length - 1, letters[0]) 
}