LeetCode-in-Java
59. Spiral Matrix II
Medium
Given a positive integer n, generate an n x n matrix filled with elements from 1 to n2 in spiral order.
Example 1:
Input: n = 3
Output: [[1,2,3],[8,9,4],[7,6,5]]
Example 2:
Input: n = 1
Output: [[1]]
Constraints:
1 <= n <= 20
Solution
public class Solution {
public int[][] generateMatrix(int n) {
int num = 1;
int rStart = 0;
int rEnd = n - 1;
int cStart = 0;
int cEnd = n - 1;
int[][] spiral = new int[n][n];
while (rStart <= rEnd && cStart <= cEnd) {
for (int k = cStart; k <= cEnd; k++) {
spiral[rStart][k] = num++;
}
rStart++;
for (int k = rStart; k <= rEnd; k++) {
spiral[k][cEnd] = num++;
}
cEnd--;
if (rStart <= rEnd) {
for (int k = cEnd; k >= cStart; k--) {
spiral[rEnd][k] = num++;
}
}
rEnd--;
if (cStart <= cEnd) {
for (int k = rEnd; k >= rStart; k--) {
spiral[k][cStart] = num++;
}
}
cStart++;
}
return spiral;
}
}