2019-07-27 59. Spiral Matrix II

Given a positive integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

Example:

Input: 3
Output:
[
[ 1, 2, 3 ],
[ 8, 9, 4 ],
[ 7, 6, 5 ]
]

idea：

 public int[][] generateMatrix(int n) {
            //获得总数
            int total = n * n;
            //确定边界：上下左右
            int u = 0, d = n - 1, l = 0, r = n - 1;
            int i = 1;
            int[][] ints = new int[n][n];
            while (i <= total) {
                //左到右
                for (int j = l; j <= r; j++) {
                    ints[l][j] = i++;
                }
                
                u++;
                //上到下
                for (int j = u; j <= d; j++) {
                    ints[j][r] = i++;

                }
                r--;
                //右到左
                for (int j = r; j >= l; j--) {
                    ints[d][j] = i++;

                }
                d--;
                //下到上
                for (int j = d; j >= u; j--) {
                    ints[j][l] = i++;
                }
                l++;
            }
            return ints;      
    }

借用别人的图

image.png