541. Reverse String II

Given a string and an integer k, you need to reverse the first k characters for every 2k characters counting from the start of the string. If there are less than k characters left, reverse all of them. If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and left the other as original.

Example:
Input: s = "abcdefg", k = 2
Output: "bacdfeg"

Restrictions:
- The string consists of lower English letters only.
- Length of the given string and k will in the range [1, 10000]

这个题目其实还挺麻烦的，就一点点拼凑吧。

/**
 * @param {string} s
 * @param {number} k
 * @return {string}
 */
var reverseStr = function(s, k) {
    if(k>s.length)return s.split("").reverse().join("");
    var result="";
    for(var i=0;i<Math.ceil(s.length/(2*k));i++){
        if((i*2*k+k)<s.length)result+=s.slice(i*2*k,i*2*k+k).split("").reverse().join(""); //采用提取字符串，转换为数组，反转，再拼接为字符串 的方法
        else result+=s.slice(i*2*k).split("").reverse().join("");//排除长度不足的情况
        if((i*2*k+2*k)<s.length)result+=s.slice(i*2*k+k,i*2*k+2*k);//直接提取不需要反转的字符串部分。
        else result+=s.slice(i*2*k+k);//排除长度不足的情况。
    }
    return result;
};