[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;
    }
}