541. 反转字符串 II

方法一：模拟（reverse方法分开写）

/**
 * @param {string} s
 * @param {number} k
 * @return {string}
 */
var reverseStr = function(s, k) {
    const n = s.length;
    const arr = Array.from(s);
    for (let i = 0; i < n; i += 2 * k) {
        reverse(arr, i, Math.min(i + k, n) - 1);
    }
    return arr.join('');
};

const reverse = (arr, left, right) => {
    while (left < right) {
        const temp = arr[left];
        arr[left] = arr[right];
        arr[right] = temp;
        left++;
        right--;
    }
}

方法二：reverse写一起

/**
 * @param {string} s
 * @param {number} k
 * @return {string}
 */
var reverseStr = function(s, k) {
    const len = s.length;
    let resArr = s.split("");
    for (let i = 0; i < len; i += 2 * k) {  // 每隔2k个字符的前k个字符进行反转
        let l = i - 1, r = i + k > len ? len : i + k;
        while (++l < --r) [resArr[l], resArr[r]] = [resArr[r], resArr[l]];
    }
    return resArr.join("");
};