Given a string, find the first non-repeating character in it. For example, if the input string is “GeeksforGeeks”, then output should be ‘f’ and if input string is “GeeksQuiz”, then output should be ‘G’.
We have discussed two solutions in Given a string, find its first non-repeating character . In this post a further optimized solution (over method 2 of previous post) is discussed. The idea is to optimize space. Instead of using a pair to store count and index, we use single element that store index if element appears once, else stores a negative value.
First non-repeating character is f
Time Complexity : O(n)
- Efficiently find first repeated character in a string without using any additional data structure in one traversal
- Replace every character of string by character whose ASCII value is K times more than it
- Find a string such that every character is lexicographically greater than its immediate next character
- Check if frequency of character in one string is a factor or multiple of frequency of same character in other string
- Replace every character of a string by a different character
- Lexicographically smallest string formed by appending a character from the first K characters of a given string
- Find the character in first string that is present at minimum index in second string
- Convert the string into palindrome string by changing only one character.
- Queries to find the first non-repeating character in the sub-string of a string
- Queries to find the last non-repeating character in the sub-string of a given string
- Move spaces to front of string in single traversal
- Replace a character c1 with c2 and c2 with c1 in a string S
- Change string to a new character set
- Python code to move spaces to front of string in single traversal
- Lexicographically next greater string using same character set
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to email@example.com. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.