Problem

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

Examples

Example 1:

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Input: n = 3
Output: [
	[ 1, 2, 3 ],
	[ 4, 5, 6 ],
	[ 7, 8, 9 ]
]

Example 2:

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Input: n = 4
Output: [
	[1, 2, 3, 4],
	[12, 13, 14, 5],
	[11, 16, 15, 6],
	[10, 9, 8, 7]
]

Similar Problems

Solution

Method 1 - Iterative just checking boundaries

We can reuse the solution from Spiral Matrix 1 - Return#Method 1 - Iterative just checking boundaries.

Code

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public class Solution {
	public int[][] generateMatrix(int n) {
		int[][] ans = new int[n][n];
	
		int num = 1;
		
		int top = 0;
		int bottom = n - 1;
		int left = 0;
		int right = n - 1;
	
		while (num <= n * n) {
			for (int i = left; i<= right; i++) {
				ans[top][i] = num++;
			}
			top++;
	
			for (int i = top; i<= bottom; i++) {
				ans[i][right] = num++;
			}
			right--;
				//prevent duplicate row
			if (top <= bottom) {
				for (int i = right; i >= left; i--) {
					ans[bottom][i] = num++;
				}
				bottom--;
			}
			
			// prevent duplicate column
			if (left <= right) {
				for (int i = bottom; i >= top; i--) {
					ans[i][left] = num++;
				}
				left++;
			}
		}
	
		return ans;
	}
}