Dijkastra算法

Dijkstra(G,w,s)
    initialize_single_source(G,s)
    S is an empty container
    Q=G.v
    while Qis not empty
        u=extract_min(Q)
        S=S+u
        for each vertex v in G.Ajd[u]
            relax(u,v,w)

在C++语言的实现中，Q不是使用的优先队列，而是使用list，便于从中删除元素，但是每次定位元素都需要遍历list，但是因为每次需要删除元素，无法通过索引确定需要的元素，即使使用vector，仍然需要遍历vector，所以使用list更具优势。G使用vector跟随list同步更新，当list为空是，G的更新完成。

Q不能使用priority_queue是因为如果要定位某个元素，不便于遍历队列

补充几点在今天变成中遇到的知识点：

• 两条线段AB(a,b),CD(c,d),判断两条线段没有重叠的部分（a>d||b<c)
• <climits>

<climits> This header defines constants with the limits of fundamental integral types for the specific system and compiler implementation used. The limits for fundamental floating-point types are defined in <cfloat> (<float.h>). The limits for width-specific integral types and other typedef types are defined in <cstdint> (<stdint.h>).

• greater&less,使用方法是priority_queue<int,greater<int> > que,或者sort(v.begin(),v.end(),greater<int>())

  std::greater
  Function object class for greater-than inequality comparison
  Binary function object class whose call returns whether its first argument compares greater than the second (as returned by operator >).
  
  Generically, function objects are instances of a class with member function operator() defined. This member function allows the object to be used with the same syntax as a function call.