README.md

744. Find Smallest Letter Greater Than Target

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.

Solutions (Rust)

1. Linear Scan

impl Solution {
    pub fn next_greatest_letter(letters: Vec<char>, target: char) -> char {
        for &ch in &letters {
            if ch > target {
                return ch;
            }
        }
        letters[0]
    }
}

2. Binary Search

impl Solution {
    pub fn next_greatest_letter(letters: Vec<char>, target: char) -> char {
        match letters.binary_search(&target) {
            Ok(i) => letters[(i + 1) % letters.len()],
            Err(i) => letters[i % letters.len()],
        }
    }
}