Question

我正在尝试在Javascript中实现DLX，而且我遇到了更新自引用对象文字的问题。

此函数采用二进制矩阵并返回一个矩阵，其中矩阵的每个“1”都是一个对象，引用它在所有基本方向上都是“1”。

cascade={"persist"}

之前我遇到了一个问题，当我遇到在对象文字声明and was suggested to use getters中创建自引用的问题时。现在在DLX中，数据结构中的对象需要能够更改。 如何创建可编辑的自引用对象文字？

我相信这个问题可以简化为

export const constructDataObjects = matrix => {
  for (let i = 0; i < matrix.length; i++) {
    for (let j = 0; j < matrix.length; j++) {
      let u = j - 1;
      let d = j + 1;
      let l = i - 1;
      let r = i + 1;

      if (matrix[i][j] === 0) continue;

      // Check edge cases.
      if (u < 0) u = matrix.length - 1;
      if (d >= matrix.length) d = 0;
      if (l < 0) l = matrix.length - 1;
      if (r >= matrix.length) r = 0;

      // Increment and decrement directions, with bound checks.
      // On hitting a bound, circle around and start from the other side.
      while (matrix[i][u] === 0) u = u - 1 < 0 ? matrix.length - 1 : u - 1;
      while (matrix[i][d] === 0) d = d + 1 >= matrix.length ? 0 : d + 1;
      while (matrix[l][j] === 0) l = l - 1 < 0 ? matrix.length - 1 : l - 1;
      while (matrix[r][j] === 0) r = r + 1 >= matrix.length ? 0 : r + 1;


      matrix[i][j] = {
        _u: undefined,
        _d: undefined,
        _l: undefined,
        _r: undefined,
        get u () { return this._u },
        set u (v) { return this._u = v },
        get d () { return this._d },
        set d (v) { return this._d = v },
        get l () { return this._l },
        set l (v) { return this._l = v },
        get r () { return this._r },
        set r (v) { return this._r = v },
        c : null,
        debug: `i:${i}, j:${j}, u:${u}, d:${d}, l:${l}, r:${r}`
      };
      matrix[i][j].u = matrix[i][u]
      matrix[i][j].d = matrix[i][d]
      matrix[i][j].l = matrix[l][j]
      matrix[i][j].r = matrix[r][j]

    }
  }

  return matrix;
};

为清楚起见，我将let a = arr => { for(let i = 0; i < arr.length; i++) { arr[i] = { curr: arr[i], first: arr[0], last: arr[arr.length - 1], } } return arr } console.log(a([1,2]))表示为*first中对象的引用和arr[0]作为*second中对象的引用。

现在arr[1]生成

a([1,2])

我想要的是

[ { curr: 1, first: 1, last: 2 },
  { curr: 2, first: *first, last: 2 } ]

添加getters

[ { curr: *first, first: *first, last: *second } },
  { curr: *second, first: *first, last: *second } ]

现在let a = arr => { for(let i = 0; i < arr.length; i++) { arr[i] = { get curr () { return arr[i] }, get first () { return arr[0] }, get last () { return arr[arr.length - 1] } } } return arr } console.log(a([1,2]))产生我想要的东西

a([1,2])

让我们添加更新对象的功能。这是我被困的地方。这是我尝试过的，它不起作用：

[ { curr: *first, first: *first, last: *second } },
  { curr: *second, first: *first, last: *second } ]

从控制台输出let a = arr => { for(let i = 0; i < arr.length; i++) { arr[i] = { _curr: undefined, _first: undefined, _last: undefined, get curr () { return this._curr }, set curr (v) { this._curr = v }, get first () { return this._first }, set first (v) { this._first = v }, get last () { return this._last }, set last (v) { this._last = v }, } arr[i].curr = arr[i] arr[i].first = arr[0] arr[i].last = arr[arr.length - 1] } return arr } console.log(a([1,2]))可以看出

a([1,2])

我想要的是

[ { curr: *first, first: *first, last: 2 },
  { curr: *second, first: *first, last: *second } ]

如何通过使用getter来保持行为，同时还允许对象可更新？

Answer 1

在创建该对象之前，不能创建引用对象的属性。我建议你给每个单元格一个getter方法（或属性），它在调用时访问下一个单元格，而不是在构造单元格时。

export function constructDataObjects(matrix) {
  const size = matrix.length; // assumed quadratic
  for (let i = 0; i < size; i++) {
    for (let j = 0; j < size; j++) {
      if (matrix[i][j] === 0) continue;

      // Increment and decrement directions, with bound checks.
      // On hitting a bound, circle around and start from the other side.
      let u = j;
      do { u--; if (u < 0) u = size - 1; } while (matrix[i][u] === 0);
      let d = j;
      do { d++; if (d >= size) d = 0; } while (matrix[i][d] === 0);
      let l = i;
      do { l--; if (l < 0) l = size - 1; } while (matrix[l][j] === 0);
      let r = i;
      do { r++; if (r >= size) r = 0; } while (matrix[r][j] === 0);

      matrix[i][j] = {
        u,
        d,
        l,
        r,
        getUp()    { return matrix[i][this.u] },
        getDown()  { return matrix[i][this.d] },
        getLeft()  { return matrix[this.l][j]; },
        getRight() { return matrix[this.r][j]; },
        c : null,
        debug: `i:${i}, j:${j}, u:${u}, d:${d}, l:${l}, r:${r}`
      };
    }
  }
  return matrix;
}

或者，要真正创建循环结构，首先应使用空属性创建对象，然后再填充它们。你甚至可以避免在两个方向上进行迭代。

export function constructDataObjects(matrix) {
  const size = matrix.length; // assumed quadratic
  for (let i = 0; i < size; i++) {
    for (let j = 0; j < size; j++) {
      if (matrix[i][j] !== 0) {
        matrix[i][j] = {
          i,
          j,
          u: null,
          d: null,
          l: null,
          r: null,
          c: null
        };
      }
    }
  }
  for (let i = 0; i < size; i++) {
    let j = 0;
    while (matrix[i][j] === 0 && j < size) j++;
    const first = matrix[i][j];
    let cur = first;
    while (j < size) {
      do { j++; } while (j < size && matrix[i][j] === 0);
      const next = matrix[i][j];
      cur.d = next;
      next.u = cur;
      cur = next;
    }
    if (first) {
      cur.d = first;
      first.u = cur;
    }
  }
  for (let j = 0; j < size; j++) {
    let i = 0;
    while (matrix[i][j] === 0 && i < size) i++;
    const first = matrix[i][j];
    let cur = first;
    while (i < size) {
      do { i++; } while (i < size && matrix[i][j] === 0);
      const next = matrix[i][j];
      cur.r = next;
      next.l = cur;
      cur = next;
    }
    if (first) {
      cur.r = first;
      first.l = cur;
    }
  }
  return matrix;
}

如何更新自引用对象文字中的动态属性？

1 个答案: