First Unique Character in a String Java - The Coding Shala

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First Unique Character in a String

In this post, you will learn how to find the first unique character in a given string in Java.

Given a string, find the first non-repeating character in it and return its index. If it doesn't exist, return -1.
Examples:
s = "leetcode"

return 0.

s = "loveleetcode",
return 2.

First Unique Character in a String Solution

Approach 1:

We can use HashMap. We Count every character's frequency and store it as value. Again check with string's char and if the value in the map is one return its index.
Java Program: 

class Solution {
    public int firstUniqChar(String s) {
        Map<Character, Integer> map = new HashMap<Character, Integer>();
        for(int i = 0; i<s.length(); i++){
            char ch = s.charAt(i);
            if(map.containsKey(ch)) map.put(ch, map.get(ch)+1);
            else map.put(ch, 1);
        }
        for(int i=0;i<s.length();i++){
            if(map.get(s.charAt(i)) == 1) return i;
        }
        return -1;
    }
}

Approach 2:
We can make the string to char array. If a character's index is its last Index in the array then return its index.
Java Program: 

class Solution {
    public int firstUniqChar(String s) {
        char[] a = s.toCharArray();
  
  for(int i=0; i<a.length;i++){
   if(s.indexOf(a[i])==s.lastIndexOf(a[i])){return i;}
  }
  return -1;
    }
}


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