Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order. For example, given n = 4,

[ [1, 2, 3, 4],

[12, 13, 14, 5],

[11, 16, 15, 6],

[10, 9, 8, 7] ]

Java代码：

public int[][] generateMatrix(int n) {
    if (n < 0) {
        return null;
    }

    int[][] result = new int[n][n];

    int xStart = 0;
    int yStart = 0;
    int num = 1;

    while (n > 0) {
        if (n == 1) {
            result[yStart][xStart] = num++;
            break;
        }

        //top - move right
        for (int i = 0; i < n - 1; i++) {
            result[xStart][yStart++] = num++;
        }

        //right - move down
        for (int i = 0; i < n - 1; i++) {
            result[xStart++][yStart] = num++;
        }

        //bottom - move left
        for (int i = 0; i < n - 1; i++) {
            result[xStart][yStart--] = num++;
        }

        //left - move up
        for (int i = 0; i < n - 1; i++) {
            result[xStart--][yStart] = num++;
        }

        xStart++;
        yStart++;
        n = n - 2;
    }

    return result;
}