1.逆转字符串

var reverseWords = function(s) {
    s = s.trim();
    let arr = [];
    arr = s.split(" ");
    arr = arr.reverse();
    let str = "";
    for(let i=0; i < arr.length; i ++) {
        if(arr[i]) {
            if(i!==arr.length-1) {
                str = str + arr[i] + " ";
            } else {
                str = str + arr[i];
            }
        }
    }
    return str;
};

2.旋转字符串

var reverseLeftWords = function(s, n) {
    let left = s.slice(0, n);
    let right = s.slice(n,s.length);
    return right+left;
};