Spiral Matrix I & II

Spiral Matrix I

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

Example

Given n = 3,

You should return the following matrix:

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

分析：
从上，右，下，左打印。

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

         int[][] arr = new int[n][n];
         int a = ;
         int b = n - ;
         int k = ;

         while (a < b) {
             for (int i = a; i <= b; i++) {
                 arr[a][i] = k++;
             }

             for (int i = a +  ; i <= b - ; i++) {
                 arr[i][b] = k++;
             }

             for (int i = b ; i >= a; i--) {
                 arr[b][i] = k++;
             }

             for (int i = b -  ; i >= a + ; i--) {
                 arr[i][a] = k++;
             }

             a++;
             b--;
         }
         // if n is odd, it will be executed, if it is even, it won't be executed.
         if (a == b) {
             arr[a][b] = k;
         }
         return arr;
     }
 }

Spiral Matrix II

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

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：

拿到左上角和右下角的坐标，然后从上，右，下，左打印。然后更新坐标。

 public class Solution {
     public List<Integer> spiralOrder(int[][] matrix) {
         List<Integer> list = new ArrayList<>();

         if (matrix == null || matrix.length ==  || matrix[].length == ) return list;
         int a = , b = ;
         int x = matrix.length - , y = matrix[].length - ;

         while (a <= x && b <= y) {
             // top row
             for (int i = b; i <= y; i++) {
                 list.add(matrix[a][i]);
             }
             // right column
             for (int i = a + ; i <= x - ; i++) {
                 list.add(matrix[i][y]);
             }
             // bottom row
             if (a != x) {
                 for (int i = y; i >= b; i--) {
                     list.add(matrix[x][i]);
                 }
             }
             // left column
             if (b != y) {
                 for (int i = x - ; i >= a + ; i--) {
                     list.add(matrix[i][b]);
                 }
             }

             a++;
             b++;
             x--;
             y--;
         }
         return list;
     }
 }