Spiral Matrix

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题目：

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：
《剑指offer》上原题，但是我记得我都ac过了啊

http://www.programcreek.com/2013/01/leetcode-spiral-matrix-java/

public class Solution {    public List<Integer> spiralOrder(int[][] matrix) {        List<Integer> result = new ArrayList<Integer>();         if(matrix == null || matrix.length == 0) return result;         int m = matrix.length;        int n = matrix[0].length;         int x=0;         int y=0;         while(m>0 && n>0){             //if one row/column left, no circle can be formed            if(m==1){                for(int i=0; i<n; i++){                    result.add(matrix[x][y++]);                }                break;            }else if(n==1){                for(int i=0; i<m; i++){                    result.add(matrix[x++][y]);                }                break;            }             //below, process a circle             //top - move right            for(int i=0;i<n-1;i++){                result.add(matrix[x][y++]);            }             //right - move down            for(int i=0;i<m-1;i++){                result.add(matrix[x++][y]);            }             //bottom - move left            for(int i=0;i<n-1;i++){                result.add(matrix[x][y--]);            }             //left - move up            for(int i=0;i<m-1;i++){                result.add(matrix[x--][y]);            }             x++;            y++;            m=m-2;            n=n-2;        }         return result;    }}

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