用于更新JSON响应中元素位置的最快算法[关闭]

Question

Considering the JSON structure bellow, I need to be able to change the position of an item. The position can be changed only in increments of 1 (so +1 or -1).

Given the fact that I always send back to the API the entire JSON and that there can be a few hundreds items in the structure, is there a known algorithm to achieve this positions change fast?

The item is searched in the structure by its id.

For example I want to update the "position" of item with "id = 2" to "1". This step is easy because I can loop through the structure and find the element by id. But where I got stuck is the step where I need to update the other items accordingly.

I'm looking to implement this in PHP or Javascript.

{
  "employees": {
    "employee": [
      {
        "id": "1",
        "firstName": "Tom",
        "lastName": "Cruise",
        "position": 1
      },
      {
        "id": "2",
        "firstName": "Maria",
        "lastName": "Sharapova",
        "position": 2
      },
      {
        "id": "3",
        "firstName": "Robert",
        "lastName": "Downey Jr.",
        "position": 3
      }
    ]
  }
}

Answer 1

If you want to change the position of an element from i to j, you need to change the positions of the elements of which position is between i to j.

var arr = [
  {
    "id": "1",
    "firstName": "Tom",
    "lastName": "Cruise",
    "position": 1
  },
  {
    "id": "2",
    "firstName": "Maria",
    "lastName": "Sharapova",
    "position": 2
  },
  {
    "id": "3",
    "firstName": "Robert",
    "lastName": "Downey Jr.",
    "position": 3
  }
]

function changePosition(from, to) {
    var startValue;
    var endValue;
    for (var l = 0; l < arr.length; l++) {
    if (arr[l].position == from) {
        startValue = arr[l].position;
    }
    if (arr[l].position == to) {
        endValue = arr[l].position;
    }
  }
    var i = Math.min(startValue, endValue);
  var j = Math.max(startValue, endValue);
  var inc = from > to ? 1 : -1;
  for (var k = 0; k < arr.length; k++) {
    if (arr[k].position >= i && arr[k].position <= j) {
        if (arr[k].position == from) {
        arr[k].position = to;
      } else {
        arr[k].position += inc;
      }
    }
  }
}

changePosition(3, 1);
console.log(arr);

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