数组全排序

输入: [1,2,3]
输出:
[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]

const permute=(arr)=>{
  const len=arr.length;
  const result;
  const backstrak=(currentIndex)=>{
    if(currentIndex===len){
      result.push(arr);
      return;
    }
    for(let i=0;i<len;i++){
        [arr[i],arr[currentIndex]]=[arr[currentIndex],arr[i]];
        backstrak(currentIndex+1);
        [arr[i],arr[currentIndex]]=[arr[currentIndex],arr[i]];
    }
  }
  return result;
}