Leetcode 题目解析之 Spiral Matrix II

    public int[][] generateMatrix(int n) {
        if (n <= 0) {
            return new int[0][0];
        }
        int[][] matrix = new int[n][n];
        int num = 1;
        int startx = 0, endx = n - 1;
        int starty = 0, endy = n - 1;
        while (startx <= endx && starty <= endy) {
            // 上边的行，从左向右
            for (int y = starty; y <= endy; y++) {
                matrix[startx][y] = num++;
            }
            // 右边的列，从上到下
            for (int x = startx + 1; x <= endx; x++) {
                matrix[x][endy] = num++;
            }
            // 如果行或列遍历完，则退出循环
            if (startx == endx || starty == endy) {
                break;
            }
            // 下边的行，从右向左
            for (int y = endy - 1; y >= starty; y--) {
                matrix[endx][y] = num++;
            }
            // 左边的列，从下到上
            for (int x = endx - 1; x >= startx + 1; x--) {
                matrix[x][starty] = num++;
            }
            startx++;
            starty++;
            endx--;
            endy--;
        }
        return matrix;
    }