Smallest Letter Greater Than Target

L5 Medium Binary Search

Concept

Binary search works on any ordered sequence; characters are no exception. For wrapping sequences, if no match is found, the answer wraps to the first element.

Given a string letters of sorted lowercase letters (duplicates allowed) and a single-character target, return the smallest character in letters that is strictly greater than target. If none exists, wrap around and return the first character.

Examples

▸ letters = "cfj", target = "a"

→ c

▸ letters = "cfj", target = "c"

→ f

▸ letters = "xxyy", target = "z"

→ x

Progressive Hints

Hint 1 · Nudge

Only the first character that strictly surpasses target matters, with wrap-around at the end.

Hint 2 · Plan

Binary search for the first index whose character is greater than target. If the search runs off the end, wrap around and return the first character.

Hint 3 · Approach

Binary search for the first index i where letters[i] > target. Return letters[i], or letters[0] when the search ends past the last index.

Output

// Run your code to see the output here.