Spiral Matrix

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

For 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].

Solution

按照题意输出即可

Complexity

时间复杂度 O(n)，空间复杂度 O(1)

Code

public class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        ArrayList<Integer> res = new ArrayList<Integer>();
        if (matrix.length == 0 || matrix[0].length == 0) return res;
        int n = matrix.length, m = matrix[0].length, row = 0, col = -1;
        while (true) {
            for (int i = 0; i < m; ++i) res.add(matrix[row][++col]);
            if (--n == 0) break;
            for (int i = 0; i < n; ++i) res.add(matrix[++row][col]);
            if (--m == 0) break;
            for (int i = 0; i < m; ++i) res.add(matrix[row][--col]);
            if (--n == 0) break;
            for (int i = 0; i < n; ++i) res.add(matrix[--row][col]);
            if (--m == 0) break;
        }
        return res;
    }
}