FirstUniqueCharacterinaString.java

package com.stevesun.solutions;

import java.util.HashMap;
import java.util.Map;
/**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.

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 */
public class FirstUniqueCharacterinaString {

    public static int firstUniqChar(String s) {
        Map<Character, Integer> countMap = new HashMap();
        Map<Character, Integer> indexMap = new HashMap();
        
        for(int i = 0; i < s.length(); i++){
            if(countMap.containsKey(s.charAt(i))){
                countMap.put(s.charAt(i), countMap.get(s.charAt(i))+1);
            } else {
                indexMap.put(s.charAt(i), i);
                countMap.put(s.charAt(i), 1);
            }
        }
        
        for(int i = 0; i < s.length(); i++){
            if(countMap.get(s.charAt(i)) == 1) return indexMap.get(s.charAt(i));
        }
        return -1;
    }
    
    public static void main(String...strings){
        String s = "leetcode";
        System.out.println(firstUniqChar(s));
    }

}