Remove duplicates from string in place in O(n).

# Python program to remvoe duplicate characters from an 
# input string 
NO_OF_CHARS = 256

# Since strings in Python are immutable and cannot be changed 
# This utility function will convert the string to list 
def toMutable(string): 
	List = [] 
	for i in string: 
		List.append(i) 
	return List

# Utility function that changes list to string 
def toString(List): 
	return ''.join(List) 

# Function removes duplicate characters from the string 
# This function work in-place and fills null characters 
# in the extra space left 
def removeDups(string): 
	bin_hash = [0] * NO_OF_CHARS 
	ip_ind = 0
	res_ind = 0
	temp = '' 
	mutableString = toMutable(string) 

	# In place removal of duplicate characters 
	while ip_ind != len(mutableString): 
		temp = mutableString[ip_ind] 
		if bin_hash[ord(temp)] == 0: 
			bin_hash[ord(temp)] = 1
			mutableString[res_ind] = mutableString[ip_ind] 
			res_ind+=1
		ip_ind+=1

	# After above step string is stringiittg. 
	# Removing extra iittg after string 
	return toString(mutableString[0:res_ind]) 

# Driver program to test the above functions 
string = "geeksforgeeks"
print(removeDups(string)) 

# A shorter version for this program is as follows 
# import collections 
# print ''.join(collections.OrderedDict.fromkeys(string)) 

# This code is contributed by Bhavya Jain