In this section we are going to find the first unique or non-repeating character from a string or stream of characters. There are multiple ways to solve this problem. We will try to create two different program for the same stream of characters.
Method 1: Using function
def firstNonRepeatingChar(str1):
char_order = []
counts = {}
for c in str1:
if c in counts:
counts[c] += 1
else:
counts[c] = 1
char_order.append(c)
for c in char_order:
if counts[c] == 1:
return c
return None
print(firstNonRepeatingChar('PythonforallPythonMustforall'))
print(firstNonRepeatingChar('tutorialspointfordeveloper'))
print(firstNonRepeatingChar('AABBCC'))
Result
M
u
None
Above program give O(n) solution. In above program we first loop through the string once. Once we find a new character, we store it in counts object with a value of 1 and append it to char_order. When we come across a repeated character, we increment the value of counts by 1. Finally, we loop through char_order until we find a character with a value of 1 in char_order and return it.
Method 2: Using while loop
s = "tutorialspointfordeveloper"
while s != "":
slen0 = len(s)
ch = s[0]
s = s.replace(ch, "")
slen1 = len(s)
if slen1 == slen0-1:
print ("First non-repeating character is: ",ch)
break;
else:
print ("No Unique Character Found!")
Result
First non-repeating character is: u