顺时针打印矩阵

vector<int> printMatrix(vector<vector<int>> matrix) {
        int M = matrix[0].size();
        int N = matrix.size();
        int left=0,right=M-1,top=0,bot=N-1;
        vector<int> result;
        while(left<=right && top<=bot)
        {
            //to right
            for(int i=left; i<=right;++i)
                result.push_back(matrix[top][i]);
            //to down
            for(int i=top+1;i<=bot;i++)
                result.push_back(matrix[i][right]);
            //to left
            if(bot!=top)
            for(int i=right-1;i>=left;--i)
                result.push_back(matrix[bot][i]);
            //to up
            if(left!=right)
            for(int i=bot-1;i>top;i--)
                result.push_back(matrix[i][left]);
            
            left++; right--;top++;bot--;
        }
        return result;
    }