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export default function ladderLength(    beginWord: string,    endWord: string,    wordList: string[],): number {    const words = new Set(wordList);    if (!words.has(endWord)) return 0;
    if (beginWord.length === 1) return 2;
    let current = new Set([beginWord]);
    let rightcurrent = new Set([endWord]);    words.delete(endWord);    let step = 1;    while (current.size) {        if (current.size > rightcurrent.size) {            [current, rightcurrent] = [rightcurrent, current];        }
        const temp: Set<string> = new Set();
        for (const word of current) {            for (const right of rightcurrent) {                if (diffOneChar(word, right)) {                    return step + 1;                }            }            for (const other of words) {                if (diffOneChar(other, word)) {                    temp.add(other);
                    words.delete(other);                }            }        }
        if (temp.size === 0) return 0;        current = temp;        step = step + 1;    }
    return 0;}
function diffOneChar(word1: string, word2: string): boolean {    let changes = 0;    for (let i = 0; i < word1.length; i++) {        if (word1[i] != word2[i]) changes += 1;    }    return changes === 1;}