[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 ]
]

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思路：在Spiral Matrix的基础上进行修改，还是dfs

class Solution {
enum direct{RIGHT = 0, DOWN, LEFT, UP};
vector<int> m_res;
vector<vector<int> > m_matrix;
vector<vector<bool> > m_valid;
int m_cnt;
public:
void dfs(int i, int j, enum direct d)
{
int row = m_matrix.size();
int col = m_matrix[0].size();

//cout << i <<",\t" << j << endl;
m_cnt++;
m_matrix[i][j] = m_cnt;
m_valid[i][j] = false;

if(d == RIGHT)
{
if( j <= col-2 && m_valid[i][j+1])
dfs(i, j+1, RIGHT);
else if(i <= row-2 && m_valid[i+1][j])
dfs(i+1, j, DOWN);
}
else if(d == DOWN)
{
if(i <= row-2 && m_valid[i+1][j])
dfs(i+1, j, DOWN);
else if(j >= 1 && m_valid[i][j-1])
dfs(i, j-1, LEFT);
}
else if(d == LEFT)
{
if(j >= 1 && m_valid[i][j-1] )
dfs(i, j-1, LEFT);
else if(i >= 1 && m_valid[i-1][j])
dfs(i-1, j, UP);
}
else if(d == UP)
{
if(i >= 1 && m_valid[i-1][j])
dfs(i-1, j, UP);
else if(j <= col-1 && m_valid[i][j+1])
dfs(i, j+1, RIGHT );
}
}
public:
vector<vector<int> > generateMatrix(int n)
{
if(n == 0)
return m_matrix;

// construct the matrix
vector<int> row(n, 0);
m_matrix.resize(n, row);
//for(int i = 0; i < n; i++)
//    m_matrix.push_back(row);

vector<bool> valid(n, true);
m_valid.resize(n, valid);
//for(int i = 0; i < n; i++)
//    m_valid.push_back(valid);

m_cnt = 0;

dfs(0, 0, RIGHT);

return m_matrix;
}
};