Efficient datastructure

What is the best data structure for the following problem?

a=["how","are","you"] b=["are","you","okay"]

given these two lists i want to construct a directed graph like

how->are->you->okay

Requirements

1. I want to store a data in the nodes


2. I want to assign a weight to the edges


3. I want to find the data stored in node,given the key(eg 'how')


4. I want to get the edge weight,given the nodes to which the edge is connected(eg given 'how' and 'are',I want to know the edge weight)