如何ArrayList的元素转移到一个二维数组？ [英] How to transfer arrayList elements into a 2D array?

问题描述

我有一个的ArrayList 名为列表＆LT;对GT＆; patternList =新的ArrayList＆LT;＆GT;（）包含了一些长度为2的模式，例如，对于A = {1,2,3,4}我创造一些像模式（1,3 ）（3,2）...等。我希望把这些模式成一个二维数组（矩阵）[A] [A]的方式，模式必须进入一个特定的指数矩阵，比如图案（1,3）必须进入指数[3] [ 3]或图案（3,2）必须在[2] [2]。

I have an ArrayLists called List<Pair> patternList = new ArrayList<>() that contains a number of patterns of length 2. for example, for A={1,2,3,4} I create some patterns like (1,3)(3,2)...etc. I want to put these patterns into a 2d array(matrix)[A][A] in way that the patterns must go into a specific index in the matrix, For instance pattern (1,3) must go into index [3][3] or pattern (3,2) must go in [2][2].

感谢。

推荐答案

如果您只想把他们的第二个索引。 （编辑允许多个每个索引）：

If you just want to put them in by the second index. (edited to allow multiple per index):

List<Pair>[][] matrix = new LinkedList<Pair>[5][5]; //Replace 5 here a getter for the maximum value of A
                                  //Here it's 5 because the max of your example is 4.
//Initialize all positions of matrix to empty list.
for (int r = 0; r < matrix.length; r++){
    for(int c = 0; c < matrix[r].length; c++){
        matrix[r][c] = new LinkedList<Pair>();
    }
}
for (Pair p : patternList){
    if (matrix[p.second][p.second] == null)
        matrix[p.second][p.second] = new LinkedList<Pair>();
    matrix[p.second][p.second].add(p);
}

这是不是真的使用阵列虽然的2D方面;你可以完成同样的事情用列表的一维数组：

This isn't really using the 2d aspect of the array though; you could accomplish exactly the same thing with a 1d array of lists:

List<Pair>[] arr = new LinkedList<Pair>[5]; //Replace 5 here a getter for the maximum value of A
                                  //Here it's 5 because the max of your example is 4.
//Initialize all positions of array to empty list.
for (int r = 0; r < matrix.length; r++){
    arr[r] = new LinkedList<Pair>();
}
for (Pair p : patternList){
    if (arr[p.second] == null)
        arr[p.second] = new LinkedList<Pair>();
    arr[p.second].add(p);
}

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