【LeetCode-算法】59. 螺旋矩阵Ⅱ（Java实现）

题目

给定一个正整数 n，生成一个包含 1 到 n2 所有元素，且元素按顺时针顺序螺旋排列的正方形矩阵。

示例

输入: 3
输出:
[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

代码实现

class Solution {
    public int[][] generateMatrix(int n) {
        int[][] result = new int[n][n];

        if (n < 1) {
            return result;
        }

        int top = 0, right = n - 1, buttom = n - 1, left = 0;
        int i = 1;
        int size = n * n;

        while (size > 0) {
            // from left to right
            for (int col = left; col <= right; col++) {
                result[top][col] = i;
                size--;
                i++;
            }
            top++;

            // from top to buttom
            if (size > 0) {
                for (int row = top; row <= buttom; row++) {
                    result[row][right] = i;
                    size--;
                    i++;
                }
                right--;
            }

            // from right to left
            if (size > 0) {
                for (int row = right; row >= left; row--) {
                    result[buttom][row] = i;
                    size--;
                    i++;
                }
                buttom--;
            }

            // from buttom to top
            if (size > 0) {
                for (int col = buttom; col >= top; col--) {
                    result[col][left] = i;
                    size--;
                    i++;
                }
                left++;
            }
        }

        return result;
    }
}

执行结果

运行结果

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