[LeetCode]Spiral Matrix

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].

解题思路：

 1 class Solution {
 2 public:
 3     vector<int> spiralOrder(vector<vector<int>>& matrix) {
 4         vector<int> result;
 5         if (matrix.size() == 0) {
 6             return result;
 7         }
 8         int left = 0;
 9         int right = matrix[0].size() - 1;
10         int up = 0;
11         int down = matrix.size() - 1;
12         
13         int n = matrix.size() * matrix[0].size();
14         
15         while (true) {
16             for (int i = left; i <= right; ++i) {
17                 result.push_back(matrix[up][i]);
18                 --n;
19             }
20             if (n <= 0) {
21                 break;
22             }
23             
24             up += 1;
25             for (int i = up; i <= down; ++i) {
26                 result.push_back(matrix[i][right]);
27                 --n;
28             }
29             if (n <= 0) {
30                 break;
31             }
32             
33             right -= 1;
34             for (int i = right; i >= left; --i) {
35                 result.push_back(matrix[down][i]);
36                 --n;
37             }
38             if (n <= 0) {
39                 break;
40             }
41         
42             down -= 1;
43             for (int i = down; i >= up; --i) {
44                 result.push_back(matrix[i][left]);
45                 --n;
46             }
47             left += 1;
48             
49             if (n <= 0) {
50                 break;
51             }
52         }
53         
54         return result;
55     }
56 };