python depth first search

1# left to right, pre-order depth first tree search, iterative. O(n) time/space
2def depthFirstSearch(root):
3    st = [root]
4    while st:
5        current = st.pop()
6        print(current)
7        if current.right is not None: st.append(current.right) 
8        if current.left is not None: st.append(current.left)

1###############
2#The Algorithm (In English):
3
4# 1) Pick any node. 
5# 2) If it is unvisited, mark it as visited and recur on all its 
6#    adjacent nodes. 
7# 3) Repeat until all the nodes are visited, or the node to be 
8#    searched is found.
9
10
11# The graph below (declared as a Python dictionary)
12# is from the linked website and is used for the sake of
13# testing the algorithm. Obviously, you will have your own
14# graph to iterate through.
15graph = {
16    'A' : ['B','C'],
17    'B' : ['D', 'E'],
18    'C' : ['F'],
19    'D' : [],
20    'E' : ['F'],
21    'F' : []
22}
23
24visited = set() # Set to keep track of visited nodes.
25
26
27##################
28# The Algorithm (In Code)
29
30def dfs(visited, graph, node):
31    if node not in visited:
32        print (node)
33        visited.add(node)
34        for neighbour in graph[node]:
35            dfs(visited, graph, neighbour)
36            
37# Driver Code to test in python yourself.
38# Note that when calling this, you need to
39# call the starting node. In this case it is 'A'.
40dfs(visited, graph, 'A')
41
42# NOTE: There are a few ways to do DFS, depending on what your
43# variables are and/or what you want returned. This specific
44# example is the most fleshed-out, yet still understandable,
45# explanation I could find.

1# tree level-by-level traversal. O(n) time/space
2def breadthFirstSearch(root):
3    q = [root]
4
5    while q:
6        current = q.pop(0)
7        print(current)
8        if current.left is not None: q.append(current.left)
9        if current.right is not None: q.append(current.right)

1    DFS-iterative (G, s):                                   //Where G is graph and s is source vertex
2      let S be stack
3      S.push( s )            //Inserting s in stack 
4      mark s as visited.
5      while ( S is not empty):
6          //Pop a vertex from stack to visit next
7          v  =  S.top( )
8         S.pop( )
9         //Push all the neighbours of v in stack that are not visited   
10        for all neighbours w of v in Graph G:
11            if w is not visited :
12                     S.push( w )         
13                    mark w as visited
14
15
16    DFS-recursive(G, s):
17        mark s as visited
18        for all neighbours w of s in Graph G:
19            if w is not visited:
20                DFS-recursive(G, w)

1# HAVE USED ADJACENY LIST
2class Graph:
3    def __init__(self,lst=None):
4        self.lst=dict()
5        if lst is None:
6            pass
7        else:
8            self.lst=lst
9    def find_path(self,start,end):
10        self.checklist={}
11        for i in self.lst.keys():
12            self.checklist[i]=False
13        self.checklist[start]=True
14        store,extra=(self.explore(start,end))
15        if store==False:
16            print('No Path Found')
17        else:
18            print(extra)
19    def explore(self,start,end):
20        while True:
21            q=[]        
22            #print(self.checklist,q)
23            q.append(start)
24            flag=False            
25            for i in self.lst[start]:
26                if i==end:
27                    q.append(i)
28                    return True,q
29                if self.checklist[i]:
30                    pass
31                else:
32                    flag=True
33                    self.checklist[i]=True
34                    q.append(i)
35                    break   
36            if flag:
37                store,extra=self.explore(q[-1],end) 
38                if store==False:
39                    q.pop()
40                    if len(q)==0:return False
41                    return self.explore(q[-1],end)
42                elif store==None:
43                    pass
44                elif store==True:
45                    q.pop()
46                    q.extend(extra)
47                    return True,q
48            else:
49                return False,None
50    def __str__(self):return str(self.lst)
51if __name__=='__main__':
52    store={1: [2, 3, 4], 2: [3, 1], 3: [2, 1], 4: [5, 8, 1], 5: [4, 6, 7], 6: [5, 7, 9, 8], 7: [5, 6], 8: [4, 6, 9], 9: [6, 8, 10], 10: [9],11:[12,13]}
53    a=Graph(store)
54    a.find_path(1,11) # No Path Found 
55    a.find_path(1,6)# [1, 4, 5, 6]    
56    a.find_path(3,10)   # [3, 2, 1, 4, 5, 6, 9, 10] 
57    a.find_path(4,10)# [4, 5, 6, 9, 10]
58    print(a) #

1# left to right, pre-order depth first tree search, recursive. O(n) time/space
2def depthFirstSearchRec(root):
3    if root == None: return
4    print(root)
5    depthFirstSearch(root.left)
6    depthFirstSearch(root.right)