LeetCode 59. Spiral Matrix II

59. Spiral Matrix II

Difficulty: Medium

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 ]
]

Solution

Language: Java

class Solution {
    public int[][] generateMatrix(int n) {
        if (n < 0) {
            return null;
        }
        if (n == 0) {
            return new int[][]{};
        }
        int[][] result = new int[n][n];
       
        int start = 0;
        int end = n - 1;
        int x = 0, y = -1;
        int cur = 1;
        while (start <= end) {
            while(y + 1 <= end) {
                result[x][++y] = cur++;
            }
            while(x + 1 <= end) {
                result[++x][y] = cur++;
            }
            while(y - 1 >= start) {
                result[x][--y] = cur++;
            }
            start++;
            while(x - 1 >= start) {
                result[--x][y] = cur++;
            }
            end--;
        }
        return result;
    }
}