54. Spiral Matrix - Medium

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之前寫的文章

想法

• 初始的變數沒有想出來，有了left right top和bottom就簡單了

思路

1. 定義上下左右邊界，以下的code要注意out of boundary
2. 先取top elements
3. 再取right elements
4. 注意left要小於right，top要小於bottom以防special case
5. 再取bottom elements
6. 再取left elements
7. 反覆直到全部都取到

Code

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new ArrayList();
        
        // Defining boundaries
        int left = 0, right = matrix[0].length;
        int top = 0, bottom = matrix.length;

        while (left < right && top < bottom) {
            // Get top row elements
            for (int i = left; i < right; ++i) {
                res.add(matrix[top][i]);
            }
            // Shrink the area
            top += 1;

            // Get the right col elements
            for (int i = top; i < bottom; ++i) {
                // Aware out of bound, so right - 1
                res.add(matrix[i][right - 1]);
            }
            right -= 1;

            // Check for special case
            // Such as, [[1],[2],[3]]
            if (!(left < right && top < bottom)) break;

            // Get the bottom row elements
            for (int i = right - 1; i > left - 1; --i) {
                res.add(matrix[bottom - 1][i]);
            }
            bottom -= 1;

            // Get the left col elements
            for (int i = bottom - 1; i > top - 1 ; --i) {
                res.add(matrix[i][left]);
            }
            left += 1;
        }

        return res;
        
    }
}