Spiral Matrix II <leetcode>

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 ]
]

]
算法：分四个方向，右下左上，分别扫描，能填数字就填，不能填就改变方向，该题不难，但是容易有小错误，代码如下：

class Solution {
public:
    vector<vector<int>> result;
    vector<vector<int> > generateMatrix(int n) {
        int total=n*n;
        int x=0;
        int y=0;
        int direction=0;
        result.clear();
        for(int i=0;i<n;i++)
        {
            vector<int> nn;
            result.push_back(nn);
            for(int j=0;j<n;j++)
            {
                result[i].push_back(0);
            }
        }
        for(int i=1;i<=total;i++)
        {
            if(0==result[x][y])
            {
                result[x][y]=i;
            }
            else if(0==direction)
            {
                if(y+1<=n-1&&0==result[x][y+1])
                {
                  result[x][y+1]=i;
                  y++;
                }
                else 
                {
                    direction=1;
                
                    i--;
                }
            }
            else if(1==direction)
            {
                if(x+1<=n-1&&0==result[x+1][y])
                {
                   result[x+1][y]=i;
                   x++;
                }
                else
                {
                    direction=2;
                    i--;
                }
            }
            else if(2==direction)
            {
                if(y-1>=0&&0==result[x][y-1])
                {
                    result[x][y-1]=i;
                    y--;
                }
                else
                {
                    direction=3;
                    i--;
                }
            }
            else if(3==direction)
            {
                if(x-1>=0&&0==result[x-1][y])
                {
                    result[x-1][y]=i;
                    x--;
                }
                else
                {
                    direction=0;
                    i--;
                }
            }
        }
        return result;
    }
};