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745. Find Smallest Letter Greater Than Target

Array Binary Search

Problem - Find Smallest Letter Greater Than Target

Easy

You are given an array of characters letters that is sorted in non-decreasing order, and a character target. There are at least two different characters in letters.

Return the smallest character in letters that is lexicographically greater than target. If such a character does not exist, return the first character in letters.

 

Example 1:

Input: letters = ["c","f","j"], target = "a"
Output: "c"
Explanation: The smallest character that is lexicographically greater than 'a' in letters is 'c'.

Example 2:

Input: letters = ["c","f","j"], target = "c"
Output: "f"
Explanation: The smallest character that is lexicographically greater than 'c' in letters is 'f'.

Example 3:

Input: letters = ["x","x","y","y"], target = "z"
Output: "x"
Explanation: There are no characters in letters that is lexicographically greater than 'z' so we return letters[0].

 

Constraints:

  • 2 <= letters.length <= 104
  • letters[i] is a lowercase English letter.
  • letters is sorted in non-decreasing order.
  • letters contains at least two different characters.
  • target is a lowercase English letter.

Solutions

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class Solution:
    def nextGreatestLetter(self, letters: List[str], target: str) -> str:
        n = len(letters)
        left, right = 0, n - 1

        while right >= left:
            mid = (left + right) // 2
            if letters[mid] > target:
                right = mid - 1
            else:
                left = mid + 1
        return letters[left % n]

Submission Stats:

  • Runtime: 0 ms (100.00%)
  • Memory: 19.2 MB (32.41%)