[英]Dijkstra’s Algorithm issue and key error in python
Trying to code Dijkstras algorithm from this psuedocode: 尝试从此伪代码编码Dijkstras算法:
1: procedure ShortestPath
2: for 0 ≤ i ≤ n do
3: L(vi) = ∞
4: end for
5: L(a) = 0
6: S = ∅
7: while z /∈ S do
8: u = vertex not in S with L(u) minimal
9: S = S ∪ {u}
10: for v /∈ S do
11: if L(u) + µ(uv) < L(v) then
12: L(v) = L(u) + µ(uv)
13: end if
14: end for
15: end while
16: return L(z)
17: end procedure
The code I have written is this: 我写的代码是这样的:
from math import inf
def dijkstras(G,start,stop):
L = {}
for i in G[0]:
L[i] = inf
L[start] = 0
visited = []
print(L)
while stop not in visited:
u = inf
for i in L:
if L[i] < u and L[i] not in visited:
u = L[i]
break
visited.append(u)
for v in G[0]:
if v in visited:
continue
if {u,v} or {v,u} in G[1]:
for i in G[1]:
if {u,v} or {v,u} == i[0]:
weight = i[1]
break
else:
weight = inf
if L[u] + weight < L[v]:
L[v] = L[u] + weight
return stop
It gives me KeyError = 0, I Presume this is to do with line L[v] = L[u] + weight. 它给我KeyError = 0,我认为这与线L [v] = L [u] +权重有关。 Other than that I think the code is correct.
除此之外,我认为代码是正确的。 If anyone spots the issue please let me know, cheers.
如果有人发现问题,请让我知道。
In your code I see u = inf or u = L[...]
, yet in original pseudocode u
is a graph vertice, not weight. 在您的代码中,我看到
u = inf or u = L[...]
,但是在原始伪代码中, u
是图形顶点,而不是权重。 In other words you confused distances with vertices. 换句话说,您将距离与顶点混淆了。 Perhaps use strings to name vertices?
也许使用字符串来命名顶点?
Provide example of your graph format. 提供图形格式的示例。 Is G[1] a dictionary with transition keys?
G [1]是带有过渡键的字典吗? list of pairs of a transition with its weight?
权重的转换对列表? Looks like in different place it is interpreted differently.
看起来好像在不同的地方有不同的解释。
{u,v} or {v,u} == i[0]
is obviously error, you likely meant {u,v} == i[0] or {v,u} == i[0]
{u,v} or {v,u} == i[0]
显然是错误,您可能表示{u,v} == i[0] or {v,u} == i[0]
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