LeetCode 99 Spiral Matrix

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

For example,

Given the following matrix:

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

You should return [1,2,3,6,9,8,7,4,5].

分析：这道题按照题意转圈输出就行，关键是边界条件要处理好。

public class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new ArrayList<Integer>();
        if(matrix == null || matrix.length == 0 || matrix[0].length==0) 
            return res;
        int m = matrix.length;
        int n = matrix[0].length;
        //确定有几圈
        int cycle = m>n ? (n+1)/2 : (m+1)/2;
        int a = n, b = m;
        for(int i=0; i<cycle; i++){
            for(int column=i; column<i+a; column++)
                res.add(matrix[i][column]);
            for(int row=i+1; row< i+b; row++)
                res.add(matrix[row][i+a-1]);
            //奇数，只剩最后一行或最后一列，已经处理完，不需要在处理
            if(a==1 || b==1) break;
            for(int column=i+a-2; column>=i; column--)
                res.add(matrix[i+b-1][column]);
            for(int row=i+b-2; row>i; row--)
                res.add(matrix[row][i]);
            a -= 2;
            b -= 2;
        }
        return res;
    }
}