Java實作 LeetCode 54 螺旋矩陣

54. 螺旋矩陣

給定一個包含 m x n 個元素的矩陣（m 行, n 列），請按照順時針螺旋順序，傳回矩陣中的所有元素。

示例 1:

輸入:

[

[ 1, 2, 3 ],

[ 4, 5, 6 ],

[ 7, 8, 9 ]

]

輸出: [1,2,3,6,9,8,7,4,5]

示例 2:

輸入:

[

[1, 2, 3, 4],

[5, 6, 7, 8],

[9,10,11,12]

]

輸出: [1,2,3,4,8,12,11,10,9,5,6,7]

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> result = new LinkedList<>();
        if(matrix.length==0)    return result;
        int upBound = 0;
        int rightBound = matrix[0].length-1;
        int leftBound = 0;
        int downBound = matrix.length-1;
        while(true){
            for(int i=leftBound; i<=rightBound; ++i)    
                result.add(matrix[upBound][i]);
            if(++upBound>downBound) break;
            for(int i=upBound; i<=downBound; ++i)   
                result.add(matrix[i][rightBound]);
            if(--rightBound<leftBound)  break;
            for(int i=rightBound; i>=leftBound; --i)   
                result.add(matrix[downBound][i]);
            if(--downBound<upBound) break;
            for(int i=downBound; i>=upBound; --i)   
                result.add(matrix[i][leftBound]);
            if(++leftBound>rightBound)  break;
        }
        return result;
    }
}