哈希表

242.有效的字母异位词写的很漂亮的一次代码

/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
var isAnagram = function (s, t) {
    const map = new Map();
    for (const letter of s) {
        const cnt = map.has(letter) ? map.get(letter) : 0;
        map.set(letter, cnt + 1);
    }
    for (const letter of t) {
        if (!map.has(letter)) return false;
        const cnt = map.get(letter);
        map.set(letter, cnt - 1);
    }
    for (const [_, cnt] of map) {
        if (cnt) return false;
    }
    return true;
};

202.快乐数记得 map(number)

/**
 * @param {number} n
 * @return {boolean}
 */
var isHappy = function (n) {
    const set = new Set();

    let cur = n;

    while (cur !== 1) {
        let curArr = cur.toString().split('').map(Number);

        let afterSquareValue = curArr.reduce((pre, cur) => pre + cur * cur, 0);

        if (set.has(afterSquareValue)) return false;
        set.add(afterSquareValue);
        cur = afterSquareValue;
    }

    return true;
};