chore(Python): add depth first search (#775)

* Added depth first search algorithm in Python and updated README.md

* Added output example in Depth First Search algorithm

* bug fixes

* Fixed spelling mistake on line 1 (alorithm-> algorithm)

* Moved the file from recursion folder to graphs folder and updated README.md

Co-authored-by: Prathamesh Sahasrabuddhe <prathamesh16020@gmail.com>

algorithms/Python/README.md

@@ -27,6 +27,7 @@
 - [Recursive Insertion Sort](recursion/recursive_insertion_sort.py)
 - [Recursive Sum of n numbers](recursion/recursive-sum-of-n-numbers.py)
 
+
 ## Scheduling
 - [Interval Scheduling](scheduling/interval_scheduling.py)
 
@@ -73,6 +74,7 @@
 ## Graphs
 - [Simple Graph](graphs/graph.py)
 - [BFS SEQUENCE](graphs/bfs-sequence.py)
+- [Depth First Search](graphs/depth-first-search.py)
 
 ## Trees
 - [Binary Tree](trees/binary_tree.py)

algorithms/Python/graphs/depth-first-search.py

@@ -0,0 +1,62 @@
+# A dfs algorithm in Python
+# This is an algorithm for traversing a graph in depth first search manner
+# It is commonly used in tree/graph traversals
+# Time Complexity: O(V+E)
+# Space Complexity: O(V)
+# V is number of vertices and E is number of edges
+
+"""
+Refer the following example for output
+Graph 1: https://cdn.programiz.com/sites/tutorial2program/files/graph-dfs-step-0.png
+Graph 2: https://static.javatpoint.com/ds/images/depth-first-search-algorithm2.png
+
+"""
+
+def dfs(edges, vis, node):
+	if(vis[node]!=1):
+		vis[node] = 1
+		print(node, end = " ")
+	
+	for i in edges[node]:
+		if(vis[i]!=1):
+			dfs(edges, vis, i)
+
+
+def main():
+	""" Main Function """
+
+	#First example
+
+	graph1 = []
+	graph1.append([1,2,3])
+	graph1.append([0,2])
+	graph1.append([0,1,4])
+	graph1.append([0])
+	graph1.append([2])	
+
+	vis = []
+	for i in range(0,10):
+		vis.append(0)
+
+	print("DFS for Graph 1 is:")
+	dfs(graph1, vis, 0)
+
+	#Making visited list elements 0 for second graph
+	for i in range(0,10):
+		vis[i] = 0
+
+	graph2 = []
+	graph2.append([1, 2, 3])
+	graph2.append([3])
+	graph2.append([4])
+	graph2.append([5, 6])
+	graph2.append([5, 7])
+	graph2.append([2])
+	graph2.append([])
+	graph2.append([])
+
+	print("\n\nDFS for Graph 2 is:")
+	dfs(graph2, vis, 0)
+
+if __name__=="__main__":
+	main()