387. First Unique Character in a String

Question

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

Examples:

s = "leetcode"
return 0.

s = "loveleetcode",
return 2.

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

Solution

• Method 1: array(or hashMap)

  class Solution {
      public int firstUniqChar(String s) {
          int[] dic = new int[26];
          char[] arr = s.toCharArray();
          for(char c : arr){
              dic[c - 'a']++;
          }
          for(int i = 0; i < arr.length; i++){
              if(dic[arr[i] - 'a'] == 1) return i;
          }
          return -1;
      }
  }
  

Amazon session

class Solution {
    public int firstUniqChar(String s) {
        int[] count = new int[26];
        for(char c : s.toCharArray()){
            count[c - 'a']++;
        }
        for(int i = 0; i < s.length(); i++){
            if(count[s.charAt(i) - 'a'] == 1) return i;
        }
        return -1;
    }
}