0744 Find Smallest Letter Greater Than Target

Problem

Given an array of characters letters sorted in ascending order and a character target, return the smallest character in letters that is strictly greater than target. If no such character exists, return the first element of the array (the array wraps around).

Solution

We iterate through the array from left to right. The first character that is strictly greater than target is the answer, since the array is sorted. If no character satisfies the condition, we return the first element of the array.

Implementation in Rust

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

        letters[0]
    }
}