Spiral Matrix II

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

• Time: O(n)
• Space: O(1)

public int[][] generateMatrix(int n) {
    if (n <= 0) return new int[0][0];
    int[][] matrix = new int[n][n];
    int x = 0, y = -1, num = 1, m = n;
    while (true) {
        for (int i = 0; i < m; i++) matrix[x][++y] = num++;
        if(--n == 0) break;
        for (int i = 0; i < n; i++) matrix[++x][y] = num++;
        if(--m == 0) break;
        for (int i = 0; i < m; i++) matrix[x][--y] = num++;
        if(--n == 0) break;
        for (int i = 0; i < n; i++) matrix[--x][y] = num++;
        if(--m == 0) break;
    }
    return matrix;
}