use topological order to solve this problem

5. (3 points) You are given a directed acyclic graph G = (V, E) in which each node u E V has an associated price, denoted by price(u), which is a positive integer. The cost of a node u, denoted by cost(u), is defined to be the price of the cheapest node reachable from u (including u itself). Design an algorithm that computes cost(u) for all u E V. Give pseudocode, discuss running time, and give proof of correctness