Leetcode(59) Spiral Matrix II

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Description

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

Example:

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

解法

之前的那道题是螺旋形遍历数组，这题是螺旋形生成数组，方法都差不多，设置边界与方向，为二维数组赋值，同样注意处理1和0输入的情况。感觉第二次写这类题思路顺畅了很多呢(^_^)~

具体代码如下：

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class Solution {
    public int[][] generateMatrix(int n) {
        int[][] res = new int[n][n];
        if (n == 1) {
            res[0][0] = 1;
            return res;
        }
        int max = n * n;
        int i = 0;
        int j = 0;
        int upbond = 0;
        int lowbond = n - 1;
        int leftbond = 0;
        int rightbond = n - 1;
        int dir = 0;
        res[i][j] = 1;
        for (int k = 2; k <= max; k++) {
            switch (dir) {
                case 0: {
                    j++;
                    res[i][j] = k;
                    if (j == rightbond) {
                        dir = 1;
                        upbond++;
                    }
                    break;
                }
                case 1: {
                    i++;
                    res[i][j] = k;
                    if (i == lowbond) {
                        dir = 2;
                        rightbond--;
                    }
                    break;
                }
                case 2: {
                    j--;
                    res[i][j] = k;
                    if (j == leftbond) {
                        dir = 3;
                        lowbond--;
                    }
                    break;
                }
                case 3: {
                    i--;
                    res[i][j] = k;
                    if (i == upbond) {
                        dir = 0;
                        leftbond++;
                    }
                    break;
                }
            }
        }
        return res;
    }
}