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 ]
]
public int[][] generateMatrix(int n) {
int[][] res = new int[n][n];
int start = 0;
helper(res,start,n);
return res;
}
public void helper(int[][] res, int start, int n){
int num = 1;
while(start * 2 < n){
int endX = n - start - 1;
int endY = n - start - 1;
for(int i = start; i <= endX; i++){
res[start][i] = num++;
}
if(endY > start){
for(int i = start+1; i <= endY; i++){
res[i][endX] = num++;
}
}
if(endY > start && endX > start){
for(int i = endX - 1; i >= start; i--){
res[endY][i] = num++;
}
}
if(endY > start + 1 && endX > start){
for(int i = endY - 1; i > start; i--){
res[i][start] = num++;
}
}
start++;
}
}