387. First Unique Character in a String | LeetCode

 387. First Unique Character in a String

Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

 

Example 1:

Input: s = "leetcode"
Output: 0

Example 2:

Input: s = "loveleetcode"
Output: 2

Example 3:

Input: s = "aabb"
Output: -1

 

Constraints:

• 1 <= s.length <= 105
• s consists of only lowercase English letters.

The solution to the above question is-

class Solution {

public:

    int firstUniqChar(string s) {

        int arr[26]={0};

        queue<char>q;

        queue<int>ans;

        for(int i=0; i<s.length(); i++){

            arr[s[i]-'a']++;

            q.push(s[i]);

            ans.push(i);

            

        }

        while(true){

            if(!q.empty() && arr[q.front()-'a']>1){

                q.pop();

                ans.pop();

            }

            else{

                break;

            }

        }

        if(q.empty())return -1;

            return ans.front();

    }

};