abc全排列

function fn(str) {
  let arr = str.split("");
  let rr = [];
  if (arr.length === 0) {
    return [];
  }
  travel(arr, [], rr);
  console.log(rr);
}

function travel(arr, re, r) {
  if (arr.length === 0 || re.length === arr.length) {
    r.push(re.join(""));
    return;
  }
  for (let i in arr) {
    re.push(arr[i]);
    let _arr = [...arr];
    _arr.splice(i, 1);
    travel(_arr, re, r);
    re.pop();
  }
}
fn("abc");