[LeetCode] Spiral Matrix II

Total Accepted: 7483 Total Submissions: 24800

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 ]
]

public class Solution {
    public int[][] generateMatrix(int n) {
        int[][] matrix  = new int[n][n];
        int     level   = (n + 1) >> 1;
        int     start   = 1;
    
        // iterate through each layer
        // 1,2 3,4 5,6 7,8 (nxn && n > 1)
        for (int iter = 0; iter < level; iter++) {
            if (iter == (level - 1) && (n % 2 == 1)) {
                matrix[iter][iter] = start;
            }
            else {
                for (int i = iter; i < n - 1 - iter; i++, start++)      
                    matrix[iter][i] = start;
                for (int i = iter; i < n - 1 - iter; i++, start++)      
                    matrix[i][n - 1 - iter] = start;
                for (int i = n - 1 - iter; i > iter; i--, start++)      
                    matrix[n - 1 - iter][i] = start;
                for (int i = n - 1 - iter; i > iter; i--, start++)      
                    matrix[i][iter] = start;
            }
        }
        
        return matrix;
    }
}