[LeetCode] Problem 59 - Spiral Matrix II

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Given a positive integer n, generate a square matrix filled with elements from 1 to n^2 in spiral order.

Example

Input: 3

Output:

1
2
3
4
5
[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

Code

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private int number = 0;

public int[][] generateMatrix(int n) {
    int[][] matrix = new int[n][n];
    int start = 0;

    while (start * 2 < n) {
        generateMatrixHelper(matrix, n, start);
        start++;
    }

    return matrix;
}

private void generateMatrixHelper(int[][] matrix, int n, int start) {
    int endX = n - start - 1;
    int endY = n - start - 1;

    for (int i = start; i <= endX; i++)
        matrix[start][i] = ++number;
    
    if (endY > start) {
        for (int i = start + 1; i <= endY; i++)
            matrix[i][endX] = ++number;
    }

    if (endX > start && endY > start) {
        for (int i = endX - 1; i >= start; i--)
            matrix[endY][i] = ++number;
    }

    if (endX > start && endY > start + 1) {
        for (int i = endY - 1; i > start; i--)
            matrix[i][start] = ++number;
    }
}