[leetcode]59. Spiral Matrix II螺旋遍历矩阵2

Given a positive integer n, generate a square matrix filled with elements from 1 to n^2 in spiral order.

Example:

Input: 3

Output:

[

 [ 1, 2, 3 ],

 [ 8, 9, 4 ],

 [ 7, 6, 5 ]

]

题意：

给定n， 把1至n ^ 2所有的数，按照螺旋顺序填入方阵。

code

 /*

 Time: O(n^2)

 Space: O(n^2)

 */

 class Solution {

     public int[][] generateMatrix(int n) {

         int[][] matrix = new int[n][n];

         if (n == 0) return matrix;

         int beginX = 0, endX = n - 1;

         int beginY = 0, endY = n - 1;

         int num = 1;

         while (true) {

             for (int j = beginX; j <= endX; ++j) matrix[beginY][j] = num++;

             if (++beginY > endY) break;

             for (int i = beginY; i <= endY; ++i) matrix[i][endX] = num++;

             if (beginX > --endX) break;

             for (int j = endX; j >= beginX; --j) matrix[endY][j] = num++;

             if (beginY > --endY) break;

             for (int i = endY; i >= beginY; --i) matrix[i][beginX] = num++;

             if (++beginX > endX) break;

         }

         return matrix;

     }

 }