LeetCode：螺旋矩阵

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> result = new ArrayList<>();

        if(matrix == null || matrix.length == 0){
            return null;
        }
        //四个边界
        int top = 0;
        int bottom = matrix.length - 1;
        int left = 0;
        int right = matrix[0].length - 1;

        while(top <= bottom && left <= right){
            for(int i = left; i <=right; i++){
                result.add(matrix[top][i]); 
            }
            top++;

            for(int i = top; i <= bottom; i++){
                result.add(matrix[i][right]);
            }
            right--;
            //额外进行一次判断
            if(top <= bottom && left <= right){
                for(int i = right; i >= left; i--){
                    result.add(matrix[bottom][i]);
                }
                bottom--;
                for(int i = bottom; i >= top; i--){
                    result.add(matrix[i][left]);
                }
                left++;
            }

        }
        return result;
    }
}

这里需要注意第二个判断，防止读取重复数据。