Leetcode 17.22单词转换 dfs+回溯+剪枝

　　JAVA：

public final List<String> findLadders(String beginWord, String endWord, List<String> wordList) {
        List<String> re = new LinkedList<String>();
        Set<String> set = new HashSet<>(), his = new HashSet<>();
        boolean exit = dfs(re, set, his, beginWord, endWord, wordList);
        if (exit) re.add(0, beginWord);
        return re;
    }

    private final boolean dfs(List<String> re, Set<String> set, Set<String> his, String curr, String endWord,
                              List<String> wordList) {
        for (int i = 0; i < wordList.size(); i++) {
            String next = wordList.get(i);
            if (set.contains(next) || !this.canBeNext(curr, next) || his.contains(curr)) continue;
            set.add(next);
            re.add(next);
            if (next.equals(endWord) || dfs(re, set, his, next, endWord, wordList)) return true;
            set.remove(next);
            re.remove(re.size() - 1);
            his.add(next);
        }
        return false;
    }

    private final boolean canBeNext(String pre, String next) {
        int len = pre.length(), diff = 0;
        for (int i = 0; i < len; i++) {
            if (pre.charAt(i) != next.charAt(i)) {
                if (diff == 0) diff++;
                else return false;
            }
        }
        return diff == 0 ? false : true;
    }

　　JS:

/**
 * @param {string} beginWord
 * @param {string} endWord
 * @param {string[]} wordList
 * @return {string[]}
 */
var findLadders = function (beginWord, endWord, wordList) {
    let re = [];
    let hasRe = dfs(re, beginWord, new Set(), new Set(), endWord, wordList);
    if (hasRe) re.unshift(beginWord);
    return re;
};

var dfs = function (re, curr, set, his, endWord, wordList) {
    for (let i = 0; i < wordList.length; i++) {
        let next = wordList[i];
        if (set.has(next) || his.has(next) || !canBeNext(curr, next)) continue
        set.add(next);
        his.add(next);
        re.push(next);
        if (next == endWord || dfs(re, next, set, his, endWord, wordList)) return true;
        set.delete(next);
        re.pop();
    }
    return false;
}

var canBeNext = function (pre, next) {
    if (!pre || !next) return false;
    let len = pre.length, diff = 0;
    for (let i = 0; i < len; i++) {
        if (pre.charAt(i) != next.charAt(i)) {
            if (diff == 0) diff++;
            else return false;
        }
    }
    return diff == 1;
}