题目描述：

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].

思路：

1. 设置 direction ，表示遍历方向（向右，向下，向左，向上）；
2. 设置 left、right、top、buttom ，分别指示矩阵左边界、右边界、上边界、下边界；
3. 每遍历一个元素将其添加到 ret 中，直至 left>right 或 top>buttom 。

代码实现：

``````class Solution {
public List<Integer> spiralOrder(int[][] matrix) {
List<Integer> ret = new LinkedList<Integer>();
if(matrix.length==0){
return ret;
}
int left = 0;
int right = matrix[0].length-1;
int top = 0;
int buttom = matrix.length-1;
int direction = 1;

while(left<=right&&top<=buttom){
if(direction==1){
for(int i=left;i<=right;i++){
ret.add(matrix[top][i]);
}
top++;
direction = 2;
}else if(direction==2){
for(int i=top;i<=buttom;i++){
ret.add(matrix[i][right]);
}
right--;
direction = 3;
}else if(direction==3){
for(int i=right;i>=left;i--){
ret.add(matrix[buttom][i]);
}
buttom--;
direction = 4;
}else if(direction==4){
for(int i=buttom;i>=top;i--){
ret.add(matrix[i][left]);
}
left++;
direction = 1;
}
}

return ret;
}
}
``````

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