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export default function nextGreatestLetter(    letters: string[],    target: string,): string {    const length = letters.length;    if (target >= letters[length - 1]) {        return letters[0];    }    let low = 0,        high = length - 1;    while (low < high) {        const mid = Math.floor((high + low) / 2);        if (letters[mid] > target) {            high = mid;        } else {            low = mid + 1;        }    }    return letters[low];}