LeetCode——Spiral Matrix II

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

For example,

Given n = 

3

,
You should return the following matrix:

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

原题链接：https://oj.leetcode.com/problems/spiral-matrix-ii/
之前的一题是将螺旋结构的二维数组转成一维数组，此题正好相反，故只需将原来的位置上取下来的元素放回去。

public class SpiralMatrixII {
public static void main(String[] args) {
int[][] matrix = new SpiralMatrixII().generateMatrix(3);
for(int[] r : matrix){
for(int c : r)
System.out.print(c + "\t");
System.out.println();
}
}
public int[][] generateMatrix(int n) {
int[][] matrix = new int

;
if(n == 0)
return matrix;
int l = 0, r = matrix[0].length - 1;
int u = 0, d = matrix.length - 1;
int num = 1;
while (l <= r && u <= d) {
for (int i = l; i <= r; i++)
matrix[u][i] = num++;
u++;
if (u > d)
continue;
for (int i = u; i <= d; i++)
matrix[i][r] = num++;
r--;
if (l > r)
continue;
for (int i = r; i >= l; i--)
matrix[d][i] = num++;
d--;
if (u > d)
continue;
for (int i = d; i >= u; i--)
matrix[i][l] = num++;
l++;
}
return matrix;
}
}