Answer 1

没看懂你们的回答在答什么，原来的O(n^3)是怎样的，然后通过什么策略变成了O(n)的？

Answer 2

(function () {

  const del = (arr, index, len) => {
    if (index < 0) {
      index = arr.length - Math.abs(index);
    }
    let i = index + len;
    let result = [];


    let count = len;
    let offset = index;
    while (count--) {
      result.push(arr[offset++]);
    }

    while (i < arr.length) {
      arr[i - len] = arr[i];
      i++;
    }

    arr.length = arr.length - len;
    return result;

  }

  const insert = (arr, index, items) => {
    // arr.length = arr.length + items.length;

    let i = arr.length - 1;

    while (i >= index) {
      arr[i + items.length] = arr[i];
      i--;
    }
    i = 0;
    while (i < items.length) {
      arr[i + index] = items[i];
      i++
    }

  }
  
  Array.prototype._splice = function _splice(index, deleteCount, ...rest) {

    let arr = this;
    let removed = [];
  
    // 只有一个元素
    if (deleteCount === undefined) {
      removed = del(arr, index, arr.length - Math.abs(index));
    } else {
      removed = del(arr, index, deleteCount);
      if (rest.length) {
        insert(arr, index, rest);
      }
    }
  
  
    return removed;
  }
  var myFish = ["angel", "clown", "mandarin", "sturgeon"];
  var removed = myFish._splice(2, 0, "drum");
  console.log(myFish, removed)
  
  // 运算后的 myFish: ["angel", "clown", "drum", "mandarin", "sturgeon"]
  // 被删除的元素: [], 没有元素被删除
  
  var myFish = ['angel', 'clown', 'mandarin', 'sturgeon'];
  var removed = myFish._splice(2, 0, 'drum', 'guitar');
  console.log(myFish, removed)
  
  // 运算后的 myFish: ["angel", "clown", "drum", "guitar", "mandarin", "sturgeon"]
  // 被删除的元素: [], 没有元素被删除
  
  var myFish = ['angel', 'clown', 'drum', 'mandarin', 'sturgeon'];
  var removed = myFish._splice(3, 1);
  console.log(myFish, removed)
  
  // 运算后的 myFish: ["angel", "clown", "drum", "sturgeon"]
  // 被删除的元素: ["mandarin"]

  var myFish = ['angel', 'clown', 'drum', 'sturgeon'];
  var removed = myFish._splice(2, 1, "trumpet");
  console.log(myFish, removed)

  // 运算后的 myFish: ["angel", "clown", "trumpet", "sturgeon"]
  // 被删除的元素: ["drum"]

  var myFish = ['angel', 'clown', 'trumpet', 'sturgeon'];
  var removed = myFish._splice(0, 2, 'parrot', 'anemone', 'blue');
  console.log(myFish, removed)

  // 运算后的 myFish: ["parrot", "anemone", "blue", "trumpet", "sturgeon"]
  // 被删除的元素: ["angel", "clown"]

  var myFish = ['parrot', 'anemone', 'blue', 'trumpet', 'sturgeon'];
  var removed = myFish._splice(myFish.length - 3, 2);
  console.log(myFish, removed)

  // 运算后的 myFish: ["parrot", "anemone", "sturgeon"]
  // 被删除的元素: ["blue", "trumpet"]

  var myFish = ['angel', 'clown', 'mandarin', 'sturgeon'];
  var removed = myFish._splice(-2, 1);
  console.log(myFish, removed)

  // 运算后的 myFish: ["angel", "clown", "sturgeon"]
  // 被删除的元素: ["mandarin"]

  var myFish = ['angel', 'clown', 'mandarin', 'sturgeon'];
  var removed = myFish._splice(2);
  console.log(myFish, removed)

  // 运算后的 myFish: ["angel", "clown"]
  // 被删除的元素: ["mandarin", "sturgeon"]

})()