旋转数组

方式一: unshift

var rotate = function(nums, k) {
    nums.unshift(...nums.splice(nums.length - k))
    return nums;
};

方式二: splice

 var rotate = function(nums, k) {
	    nums.splice(0, 0, ...nums.splice(nums.length - k));
		return nums;
	};

方式三:for + unshift

var rotate = function(nums, k) {
	    for (var i = 0; i < k; i++) {
	        nums.unshift(nums.pop())
	    }
     return nums
	};

 let arr = [1, 2, 3, 4,5]；
 rotate(arr,3);//[3, 4, 5, 1, 2]