We are given a directed acyclic graph G. For simplicity, assume the vertices of G are {1, 2, , n} and G contains m edges. The m edges are given by m tuples of the form (i, j, c), where each tuple (i, j, c) defines a directed edge of value c from vertex i to vertex j. We assume all tuples (i, j, c) satisfy 1 i < j n and c > 0. The goal of the problem is to compute a path from 1 to n with the maximum total value. Design an O(n + m)-time algorithm for the problem.