LeetCode 54. Spiral Matrix

[Woodyiiiiiii]

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]

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四个点(left, right, top, bottom)来标志一个圆环，每次都缩短。

还要注意边界情况，即剩下的中心图样不是正方形，而是线状或者一个点，所以需要判断四个点中两对对应点的关系来判断。

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new LinkedList();
        int m = matrix.length;
        if (m == 0) {
            return res;
        }
        int n = matrix[0].length;
        // if (n == 0) {
        //     return res;
        // }
        int left = 0, right = n - 1, top = 0, bottom = m - 1;
        int i = 0, j = 0;
        while (left <= right && top <= bottom) {
            for (j = left; j <= right; ++j) {
                res.add(matrix[top][j]);
            }
            if (top == bottom) {
                break;
            }
            for (i = top + 1; i <= bottom; ++i) {
                res.add(matrix[i][right]);
            }
            if (left == right) {
                break;
            }
            for (j = right - 1; j >= left; --j) {
                res.add(matrix[bottom][j]);
            }
            for (i = bottom - 1; i > top; --i) {
                res.add(matrix[i][left]);
            }
            ++left;
            ++top;
            --right;
            --bottom;
        }
        
        return res;
    }
}

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参考资料:

LeetCode原题