59.螺旋數組第二彈

Spiral Matrix II

問題描述：

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

For example,
Given n = 3,

You should return the following matrix:

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

參考答案（python）：

class Solution(object):   
    def generateMatrix(self, n):
        """
        :type n: int
        :rtype: List[List[int]]
        """
        A, lo = [], n*n+1
        while lo > 1:
            lo, hi = lo - len(A), lo
            A = [range(lo, hi)] + zip(*A[::-1])
        return A

性能：

參考答案（c++）：

class Solution {
    public:
        vector<vector<int> > generateMatrix(int n) {
            vector<vector<int> > ret( n, vector<int>(n) );
            int k = 1, i = 0;
            while( k <= n * n )
            {
                int j = i;
                    // four steps
                while( j < n - i )             // 1. horizonal, left to right
                    ret[i][j++] = k++;
                j = i + 1;
                while( j < n - i )             // 2. vertical, top to bottom
                    ret[j++][n-i-1] = k++;
                j = n - i - 2;
                while( j > i )                  // 3. horizonal, right to left 
                    ret[n-i-1][j--] = k++;
                j = n - i - 1;
                while( j > i )                  // 4. vertical, bottom to  top 
                    ret[j--][i] = k++;
                i++;      // next loop
            }
            return ret;
        }
    };

性能：