Python-通過Dijkstra計算兩點之間的最短路徑
文章是基於http://blog.csdn.net/playboyno/article/details/7832437的實現程式碼進行修改,最終實現計算兩點之間的最短路徑並把經過的點記錄下來。
1.圖和連結中的一樣。
2.程式碼
'''
file: py_Dijkstra.py
S= [{'index': 1, 'val': 0}, {'index': 3, 'val': 15}, {'index': 2, 'val': 25}, {'index': 6, 'val': 30}, {'index': 5, 'val': 40}, {'index': 4, 'val': 50}]
dist= [0, 25, 15, 50, 40, 30]
'''
#############################################
debug=0
MAX_NUM=10000
v_num=6
end=5
S=[]#[{'index': 1, 'val': 0},...]
dist=[]
pre={1:1,2:2,3:3,4:4,5:5,6:6}
route=[]
edge=[
[0,30,15,MAX_NUM,MAX_NUM,MAX_NUM],
[5,0,MAX_NUM,MAX_NUM,20,30],
[MAX_NUM,10,0,MAX_NUM,MAX_NUM,15],
[MAX_NUM,MAX_NUM,MAX_NUM,0,MAX_NUM,MAX_NUM],
[MAX_NUM,MAX_NUM,MAX_NUM,10,0,MAX_NUM],
[MAX_NUM,MAX_NUM,MAX_NUM,30,10,0]
]
#########################initial min route
def init(start):
if(debug):
print("[init]")
S.append({'index':start,'val':0})
i=0
min_dist=10000#
while(i<v_num):
dist.append(edge[start-1][i])
#find Precursor node of start
if edge[start-1][i]!=0 and min_dist>edge[start-1][i]:
min_dist=edge[start-1][i]
pre[i+1]=start
i=i+1
######################
def v_in_S(v):
i=0
while(i<len(S)):
if(v==S[i]['index']):
return "YES"
i=i+1
return "NO"
######################Add point and weight to S
def get_min():
if(debug):
print("[get_min]")
if(len(dist)<1):
return {'index':-1,'val':0}
i=0
min_val=MAX_NUM
min_index=0
while(i<len(dist)):
if(v_in_S(i+1)=="NO"):
if(dist[i] < MAX_NUM and dist[i] > 0 and min_val>dist[i]):
min_val=dist[i]
min_index=i
i=i+1
return {'index':min_index+1,'val':min_val}
######################Update min weight value or min route
def update_dist():
tmp_index=S[len(S)-1]['index']
tmp_val=S[len(S)-1]['val']
if(debug):
print("[update_dist]","tmp_index=",tmp_index,";tmp_val=",tmp_val)
i=0
while(i<v_num):
if(v_in_S(i+1)=="NO"):
i_dist=tmp_val+edge[tmp_index-1][i]
if(debug):
print("i=",i,";i_dist=",i_dist)
if(dist[i]>i_dist):
dist[i]=i_dist
pre[i+1]=tmp_index
i=i+1
if(debug):
print("after update dist:dist=",dist)
######################
def process():
if(debug):
print("[process]")
i=0
S_len=len(S)
while(v_num != S_len and i<v_num):
min_vertex=get_min()
if(debug):
print("i=",i,";min_vertex=",min_vertex)
print("len(S)=",len(S),";S=",S)
if(min_vertex['index']>0):
if(debug):
print("----BEFORE append: len(S)=",len(S),";S=",S)
S.append(min_vertex)
if(debug):
print("====AFTER append: len(S)=",len(S),";S=",S)
update_dist()
i=i+1
S_len=len(S)
######################
def py_Dijkstra(start,end):
init(start)
print "Initial:\n ","\t start=",start,"\n\t S=",S,"\n\t dist=",dist
process()
print "Result:\n","\tS=",S,"\n\tdist=",dist
#print pre
route.append(end)
tem=end
while pre[tem]!=start:
route.insert(0,pre[tem])
tem=pre[tem]
route.insert(0,start)
print 'route:',route
#############################################
if(__name__=="__main__"):
py_Dijkstra(1,4)
</pre><pre name="code" class="python">
3.結果Initial: start= 1 S= [{'index': 1, 'val': 0}] dist= [0, 30, 15, 10000, 10000, 10000] Result: S= [{'index': 1, 'val': 0}, {'index': 3, 'val': 15}, {'index': 2, 'val': 25}, {'index': 6, 'val': 30}, {'index': 5, 'val': 40}, {'index': 4, 'val': 50}] dist= [0, 25, 15, 50, 40, 30] route: [1, 3, 6, 5, 4]