有向无权图中的最长非循环路径

动态规划。鉴于它是DAG，在最长路径问题中也引用了它。

以下来自Wikipedia的代码：

algorithm dag-longest-path is    input:          Directed acyclic graph G    output:          Length of the longest path    length_to = array with |V(G)| elements of type int with default value 0    for each vertex v in topOrder(G) do        for each edge (v, w) in E(G) do if length_to[w] <= length_to[v] + weight(G,(v,w)) then     length_to[w] = length_to[v] + weight(G, (v,w))    return max(length_to[v] for v in V(G))