Algorithm-Arrays-7 Diagonals 对角线输出

1. 题目

Give a N*N square matrix, return an array of its anti-diagonals. Look at the example for more details.

Example:

Input:

1 2 3
4 5 6
7 8 9

Return the following :

[
[1],
[2, 4],
[3, 5, 7],
[6, 8],
[9]
]

2. 解答

public ArrayList<ArrayList<Integer>> diagonal(ArrayList<ArrayList<Integer>> a) {
        ArrayList<ArrayList<Integer>> result = new ArrayList<>();
        int dimension = a.size();
        for (int i = 0; i < 2 * dimension - 1; i++) {
            result.add(getDiagonal(i, a));
        }
        return result;
    }

    private ArrayList<Integer> getDiagonal(int layer, ArrayList<ArrayList<Integer>> a) {
        ArrayList<Integer> result = new ArrayList<>();
        for (int i = 0; i <= layer; i++) {
            int j = layer - i;
            // This avoids array out of boundary exception
            if (i < a.size() && j < a.size())
                result.add(a.get(i).get(j));
        }

        return result;
    }

• 另一种解法

public ArrayList<ArrayList<Integer>> superDiagonal(ArrayList<ArrayList<Integer>> a) {
        ArrayList<ArrayList<Integer>> result = new ArrayList<>();
        for (int i = 0; i < 2 * a.size() - 1; i++)
            result.add(new ArrayList<Integer>());

        // Fantastic
        for (int i = 0; i < a.size(); i++) {
            for (int j = 0; j < a.get(0).size(); j++)
                result.get(i + j).add(a.get(i).get(j));

        }
        return result;
    }