struct Solution;
impl Solution {
fn next_greatest_letter(letters: Vec<char>, target: char) -> char {
let n = letters.len();
let mut l = 0;
let mut r = n;
while l < r {
let mid = l + (r - l) / 2;
if target < letters[mid] {
r = mid;
} else {
l = mid + 1;
}
}
letters[l % n]
}
}
#[test]
fn test() {
let letters: Vec<char> = vec!['c', 'f', 'j'];
let target = 'a';
let res = 'c';
assert_eq!(Solution::next_greatest_letter(letters, target), res);
let letters: Vec<char> = vec!['c', 'f', 'j'];
let target = 'c';
let res = 'f';
assert_eq!(Solution::next_greatest_letter(letters, target), res);
let letters: Vec<char> = vec!['c', 'f', 'j'];
let target = 'd';
let res = 'f';
assert_eq!(Solution::next_greatest_letter(letters, target), res);
let letters: Vec<char> = vec!['c', 'f', 'j'];
let target = 'g';
let res = 'j';
assert_eq!(Solution::next_greatest_letter(letters, target), res);
let letters: Vec<char> = vec!['c', 'f', 'j'];
let target = 'j';
let res = 'c';
assert_eq!(Solution::next_greatest_letter(letters, target), res);
let letters: Vec<char> = vec!['c', 'f', 'j'];
let target = 'k';
let res = 'c';
assert_eq!(Solution::next_greatest_letter(letters, target), res);
}