[Leetcode] Problem 498 - Diagonal Traverse

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Given a matrix of M x N elements (M rows, N columns), return all elements of the matrix in diagonal order as shown in the below image.

Example

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

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

Explanation:

wmY5uR.png

Note

The total number of elements of the given matrix will not exceed 10,000.

Code

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public int[] findDiagonalOrder(int[][] matrix) {
    if (matrix == null || matrix.length == 0 || matrix[0].length == 0)
        return new int[0];

    int m = matrix.length;
    int n = matrix[0].length;
    int[] result = new int[m * n];
    int row = 0;
    int col = 0;
    int dir = 1;

    for (int i = 0; i < m * n; i++) {
        result[i] = matrix[row][col];
        row -= dir;
        col += dir;

        if (row >= m) {
            row = m - 1;
            col += 2;
            dir = -dir;
        }

        if (col >= n) {
            col = n - 1;
            row += 2;
            dir = -dir;
        }

        if (row < 0) {
            row = 0;
            dir = -dir;
        }

        if (col < 0) {
            col = 0;
            dir = -dir;
        }
    }

    return result;
}