[leetcode]54. Spiral Matrix螺旋矩阵

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

Example 1:

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

Example 2:

Input:
[
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9,10,11,12]
]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]

题意：

按螺旋方式遍历矩阵。

Solution1: Simulation the process and implement it.

code

 class Solution {
       public List<Integer> spiralOrder(int[][] matrix) {
         List<Integer> res = new ArrayList<>();
         if(matrix.length == 0 || matrix[0].length == 0) return res;

         int top = 0;
         int bottom = matrix.length-1;
         int left = 0;
         int right = matrix[0].length-1;

         while(true){
             for(int i = left; i <= right; i++) {
                 res.add(matrix[top][i]);
             }
             top++;
             if(left > right || top > bottom) break;

             for(int i = top; i <= bottom; i++) {
                 res.add(matrix[i][right]);
             }
             right--;
             if(left > right || top > bottom) break;

             for(int i = right; i >= left; i--) {
                 res.add(matrix[bottom][i]);
             }
             bottom--;
             if(left > right || top > bottom) break;

             for(int i = bottom; i >= top; i--){
                 res.add(matrix[i][left]);
             }
             left++;
             if(left > right || top > bottom) break;
         }
         return res;
     }
 }