[LeetCode] Spiral Matrix.java

public class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> out = new ArrayList<>();
        if (matrix.length == 0) {
            return out;
        }
        int firstRow = 0;
        int lastRow = matrix.length - 1;
        int firstColumn = 0;
        int lastColumn = matrix[0].length - 1;
        while (firstRow < lastRow && firstColumn < lastColumn) {
            for (int j = firstColumn; j <= lastColumn; j++) {
                out.add(matrix[firstRow][j]);
            }
            for (int i = firstRow + 1; i <= lastRow; i++) {
                out.add(matrix[i][lastColumn]);
            }
            for (int j = lastColumn - 1; j >= firstColumn; j--) {
                out.add(matrix[lastRow][j]);
            }
            for (int i = lastRow - 1; i > firstRow; i --) {
                out.add(matrix[i][firstColumn]);
            }
            
            firstRow++;
            lastRow--;
            firstColumn++;
            lastColumn--;
        }
        if (firstRow == lastRow) {
            for (int j = firstColumn; j <= lastColumn; j ++) {
                out.add(matrix[firstRow][j]);
            }
        } else if (firstColumn == lastColumn) {
            for (int i = firstRow; i <= lastRow; i ++) {
                out.add(matrix[i][firstColumn]);
            }
        }
        return out;
    }
}