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0744 - Find Smallest Letter Greater Than Target (Easy)

https://leetcode.com/problems/find-smallest-letter-greater-than-target

Problem Statement​

Given a characters array letters that is sorted in non-decreasing order and a character target, return the smallest character in the array that is larger than target.

Note that the letters wrap around.

  • For example, if target == 'z' and letters == ['a', 'b'], the answer is 'a'.

Example 1:

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

Example 2:

Input: letters = ["c","f","j"], target = "c"
Output: "f"

Example 3:

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

Constraints:

  • 2 <= letters.length <= 10^4
  • 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.
Prerequisite
Written by @wkw
class Solution {
public:
    char nextGreatestLetter(vector<char>& letters, char target) {
        // init possible range
        int l = 0, r = letters.size() - 1;
        while (l < r) {
            int m = l + (r - l) / 2;
            // exclude m
            if (target >= letters[m]) l = m + 1;
            // include m
            else r = m;
        }
        // handle letter wrap case
        return letters[l] > target ? letters[l] : letters[0];
    }
};