13、旋转数组

给定一个数组，将数组中的元素向右移k个位置，其中k是非负数，例如：

输入：[1,2,3,4,5,6]和k=3

输出：[5,6,1,2,3,4]

• slice

输入：[1,-100,78,90]  k = 2
输出：[90,1,-100,78]

function rotate(key){
  //参数处理，key>0
  if(key<0||key === 0||key === this.length)return this;
  if(key>this.length){key = key%this.length}
  //slice支持负数索引，直接就是数组的后几位
   return this.slice(-key).concat(this.slice(0,this.length-key))
}
Array.prototype.rotate = rotate;



let arr = [1,2,3,4,5,6,7],
        k = 3;
arr.rotate(3);        // [5, 6, 7, 1, 2, 3, 4]

slice参数：开始点，结束点，返回：切割的数组

splice参数：开始点、长度，返回：删除的这部分返回

• splice

输入：[1,-100,78,90]  k = 2
输出：[90,1,-100,78]

function rotate(key){
  //参数处理，key>0
  if(key<0||key === 0||key === this.length)return this;
  if(key>this.length){key = key%this.length}

   return this.splice(this.length-key,key).concat(this)
}
Array.prototype.rotate = rotate;



let arr = [1,2,3,4,5,6,7],
        k = 3;
arr.rotate(3);        // [5, 6, 7, 1, 2, 3, 4]

• 最后一项删除放到最开头，执行k次

输入：[1,-100,78,90]  k = 2
输出：[90,1,-100,78]

//写法一：
function rotate(key){
  //参数处理，key>0
  if(key<0||key === 0||key === this.length)return this;
  if(key>this.length){key = key%this.length}

   for(let i = 0;i<=key;i++){
     this.unshift(this.pop());        //this.pop()最后一项；unshift首部插入
   }
   return this;
}
Array.prototype.rotate = rotate;

//写法二：
function rotate(key){
  //参数处理，key>0
  if(key<0||key === 0||key === this.length)return this;
  if(key>this.length){key = key%this.length}

  new Array(k).fill('').forEach((item)=>{
    this.unshift(this.pop());        //this.pop()最后一项；unshift首部插入
  })
   return this;
}
Array.prototype.rotate = rotate;

let arr = [1,2,3,4,5,6,7],
        k = 3;
arr.rotate(3);        // [5, 6, 7, 1, 2, 3, 4]