[数据结构与算法]LeetCode-100题(Hot) 59. 螺旋矩阵 II [Java实现] [极速]

给你一个正整数?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?n x n 正方形矩阵 matrix 。

示例 1：

输入：n = 3
输出：[[1,2,3],[8,9,4],[7,6,5]]

思路其实和我写的 54.螺旋矩阵?是一致的，到了临界点转向就行了，因此直接贴代码和结果：

    public static final int RIGHT = 1;
    public static final int DOWN = 2;
    public static final int LEFT = 3;
    public static final int UP = 4;
    private int[][] result;

    public int[][] generateMatrix(int n) {
        this.result = new int[n][n];
        recursion(0, 0, 1, RIGHT, n, n*n, result);
        return result;
    }

    private static void recursion(int x, int y, int index, int direction, int width, int sum, int[][] result) {
        if (index == sum+1) return;
        result[x][y] = index;
        switch (direction) {
            case RIGHT:
                if (y+1 == width || result[x][y+1] != 0) {
                    direction = DOWN;
                    ++ x;
                } else {
                    ++ y;
                }
                break;
            case DOWN:
                if (x+1 == width || result[x+1][y] != 0) {
                    direction = LEFT;
                    -- y;
                } else {
                    ++ x;
                }
                break;
            case LEFT:
                if (y-1 == -1 || result[x][y-1] != 0) {
                    direction = UP;
                    -- x;
                } else {
                    -- y;
                }
                break;
            case UP:
                if (x-1 == -1 || result[x-1][y] != 0) {
                    direction = RIGHT;
                    ++ y;
                } else {
                    -- x;
                }
                break;
        }
        recursion(x, y, index+1, direction, width, sum, result);
    }

????????????????

?时间复杂度 O(N) 额外空间复杂度 O(1)