[LeetCode] Spiral Matrix II

题目描述:

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

For example,

Given n = 3,

You should return the following matrix:

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

解题思路:

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