在实际问题中，边的权值一般以正权的形式出现，但是很多情况下负权也是存在的。这个时候，最短路径不一定存在。我们无法得到像dijkstra算法那样时间复杂度较低的算法，但是，仍然可以用bellman-ford迭代算法去解决问题。

bellman-ford算法是迭代算法，它不像dijkstra算法，按照一定的顺序直接算出每个点的距离值，而是不断地修改每个点的当前最小距离值，直到求出真正的最短距离为止。

-In practical problems, the edge weight is generally in the form of being the right, but many cases the negative right to exist. This time, the shortest path may not exist. We can not get the algorithm dijkstra algorithm time complexity is low, but you can still use the bellman-ford iterative algorithm to solve the problem.

The bellman-ford algorithm is an iterative algorithm, it is not the dijkstra algorithm to directly calculate the distance value of each point in a certain order, but modify each point of the current minimum distance value, until you find the real shortest distance so far .