统计追加字母可以获得的单词数.js

/**
 * @param {string[]} startWords
 * @param {string[]} targetWords
 * @return {number}
 2135. 统计追加字母可以获得的单词数
 'a'.charCodeAt() // 97
 'z'.charCodeAt() // 122
 m startWords.length
 n targetWords.length
 k
 nmk的平方
 startWords = ["ant","act","tack"], targetWords = ["tack","act","acti"]
 */
var wordCount = function(startWords, targetWords) {
    let ans = 0;
    const set = new Set();
    const pos = x => x.charCodeAt() - 'a'.charCodeAt();
    for (const word of startWords) {
        let x = 0;
        for (const char of word) {
            const offset = pos(char);
            x = x | (1 << offset)
        }
        set.add(x);
    }

    for (const target of targetWords) {
        let x = 0;
        for (const char of target) {
            const offset = pos(char);
            x = x | (1 << offset)
        }
        for (const char of target) {
            // t a c k = x
            const offset = pos(char);
            const t = x ^ (1 << offset);
            if (set.has(t)) {
                ans++;
                break;
            }
        }
    }
    return ans;
};