[leetcode刷题系列]Spiral Matrix II

- - 基本上和上一道一样的道理

const int dx[] = {0, 1, 0, -1};
const int dy[] = {1, 0, -1, 0};

int n;
vector<vector<int> > ans;

void dfs(int r, int c, int p, int number){
    ans[r][c] = number;
    for(int i = 0; i < 4; ++ i){
        int nowp = p + i & 3;
        int nr = r + dx[nowp];
        int nc = c + dy[nowp];
        if(nr >= 0 && nr < n)
            if(nc >= 0 && nc < n)
                if(ans[nr][nc] == 0){
                    dfs(nr, nc, nowp, number + 1);
                    break;
                }
    }
}
class Solution {
public:
    vector<vector<int> > generateMatrix(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        ans.clear();
        if(n <= 0)
            return ans;
        ::n = n;
        ans.resize(n);
        for(int i = 0; i < n; ++ i)
            for(int j = 0; j < n; ++ j)
                ans[i].push_back(0);
        dfs(0, 0, 0, 1);
        return ans;
    }
};