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 ]]

class Solution {public:    vector
     
      
        > generateMatrix(int n) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        vector
       
        
          > result;        if (n <= 0) {            return result;        }        result.resize(n);        int i , x, begin;        for (i = 0; i < n; ++i) {            result[i].resize(n);        }        for (begin =  x = 0;;--n, ++begin) {            for (i = begin; i < n; ++i) {                result[begin][i] = ++x;            }            for (i = begin + 1;i < n; ++i) {                result[i][n - 1] = ++x;            }            if (n  <= begin) {                break;            }            for (i = n - 2; i >= begin; --i) {                result[n - 1][i] = ++x;            }            for (i = n - 2; i > begin; --i) {                result[i][begin] = ++x;            }        }        return result;       }};