【leetcode】Spiral Matrix II

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 ]
]

与Spiral Matrix相似，给定方阵的维度n，返回一个螺旋矩阵。

class Solution {
public:
    vector<vector<int> > generateMatrix(int n) {
        vector< vector<int> > matrix(n, vector<int>(n));
        //begin_row is the row number, end_row is the remaind size of each row
        int begin_row = 0, end_row = n - 1;
        //begin_col is the col number,end_col is the remaind size of each col
        int begin_col = 0, end_col = n - 1;

        int num = 1;
        while(true){
            for(int i = begin_row; i <= end_row; ++i)//left to right
                matrix[begin_row][i] = num++;
            if(++begin_col > end_col) break;

            for(int i = begin_col; i <= end_col; ++i)//up to down
                 matrix[i][end_row] = num++;
            if(begin_row > --end_row) break;

            for(int i = end_row; i >= begin_row; --i)//right to left
                matrix[end_col][i] = num++;
            if(begin_col > --end_col) break;

            for(int i = end_col; i >= begin_col; --i)//bottom to up
                matrix[i][begin_row] = num++;
            if(++begin_row > end_row) break;
        }

        return matrix;
    }
};