Find the first non-repeating character from a stream of characters in Python

Suppose we have a stream of characters, or we can consider a string and we have to find the first non-repeating character in the string. So, if the string is like “people”, the first letter whose occurrence is one is ‘o’. So, the index will be returned, that is 2 here. If there is no such character, then return -1.

To solve this, we will follow these steps −

• create one frequency map

• for each character c in string, do

  • if c is not in frequency, then insert it into frequency, and put value 1

  • otherwise increase the count in frequency

• Scan the frequency map, if the value of specific key is 1, then return that key, otherwise return -1

Example 

Let us see the following implementation to get better understanding −

 Live Demo

class Solution(object):
   def firstUniqChar(self, s):
      """
      :type s: str
      :rtype: int
      """
      frequency = {}
      for i in s:
         if i not in frequency:
            frequency[i] = 1
         else:
            frequency[i] +=1
      for i in range(len(s)):
         if frequency[s[i]] == 1:
            return i
      return -1
ob1 = Solution()
print(ob1.firstUniqChar("people"))
print(ob1.firstUniqChar("abaabba"))

Input

"people"
"abaabba"

Output

2
-1