[LeetCode] 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 = 3,

You should return the following matrix:

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

class Solution {public:    vector<vector<int> > generateMatrix(int n) {        vector<vector<int>> result;        if(n == 0)  return result;        result.resize(n);        for(int i = 0; i < n; i++)            result[i].resize(n);        int col_beg = 0, col_end = n-1;        int row_beg = 0, row_end = n-1;        int data = 1;        while(1)        {            for(int col = col_beg; col <= col_end; ++col)                result[row_beg][col] = data++;            ++row_beg;            if(data > n*n)  break;            for(int row  = row_beg; row <= row_end; ++row)                result[row][col_end] = data++;            --col_end;            if(data > n*n)  break;            for(int col = col_end; col >= col_beg; --col)                result[row_end][col] = data++;            --row_end;            if(data > n*n)  break;            for(int row = row_end; row >= row_beg; --row)                result[row][col_beg] = data++;            ++col_beg;            if(data > n*n)  break;        }        return result;    }};