顺时针打印矩阵

class Solution {
public:
    vector<int> printMatrix(vector<vector<int>> matrix) {
        vector<int> res;
        if(matrix.size()==0)
            return res;
        
        int start = 0;
        int rows = matrix.size();
        int columns = matrix[0].size();
        
        while(columns > start*2 && rows > start *2){
                printCircle(matrix,columns,rows,start,res);
                ++ start;
        }
        return res;
        
    }
    
        void printCircle(vector<vector<int>> &matrix,int columns,int rows,int start,vector<int> & res){
        int endX = columns - 1 - start;
        int endY = rows - 1 - start;
        
        for(int i = start; i <= endX; ++i){
            int number = matrix[start][i];
            res.push_back(number);
        }
        
        if(start < endY){
               for(int i = start+1;i<=endY;++i){
            int number = matrix[i][endX];
            res.push_back(number);
            }
        }
        
        if(start < endX && start < endY){
            for(int i = endX-1;i >= start;--i){
                int number = matrix[endY][i];
                res.push_back(number);
            }
        }
        
        if(start < endX && start < endY-1){
            for(int i = endY -1;i>= start +1;--i){
                int number = matrix[i][start];
                res.push_back(number);
            }
        }

    }
    
};