leetcode #59 in cpp

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 ]]

Solution:

I directly list 4 cases about how we proceed. The code is quite long but straightforward and clear.  

Code:

class Solution {public:    vector<vector<int>> generateMatrix(int n) {        vector<vector<int>> res(n,vector<int>(n,0));        int cur_row = 0;        int cur_col = 0;        int upper_row = n-1;        int lower_row = 0;        int upper_col = n-1;        int lower_col = 0;        int count = 1;        while(count<=n*n){            res[cur_row][cur_col] = count;            if(cur_row == lower_row){//at the upper row                if(cur_col == upper_col){//should turn down                    cur_row ++;                }else{//should go right                    cur_col ++;                }            }else if(cur_col == upper_col){//at the right col                if(cur_row == upper_row){//should turn left                    cur_col --;                }else{//should go down                    cur_row ++;                }            }else if(cur_row == upper_row && upper_row != lower_row){//at the bottom                if(cur_col != lower_col){//should go left                     cur_col --;                }else{//should turn up                    cur_row --;                }                            }else if(upper_col != lower_col){//cur_col == lower_col, at the left side                                    if(cur_row != lower_row + 1){//can go up                        cur_row --;                    }else{//go right to the next submatrix                        cur_col ++;                        upper_row --;                        lower_row ++;                        upper_col --;                        lower_col ++;                    }            }                        count++;        }        return res;    }};