Given a string, find the first non-repeating character in it and return it’s index. If it doesn’t exist, return -1.


s = “leetcode” return 0. s = “loveleetcode”, return 2.

Note: You may assume the string contain only lowercase letters.


Create an Array of length 26 and maintain frequency of the each character. Here ‘a’ having index as 0 and ‘z’ having index as 25. Iterate over the String and increament the value in the array.

After we build frequency Array, Just iterate a String one more time and check for each character, if frequency is 1 then that index is the answer.




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