查找首个重复字符串算法

/**
 * 例“abncdbmn”,首个重复字母为b
 */
package cn.edu.moon.alg;

import java.util.BitSet;
import java.util.HashMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * @author Administrator
 *
 */
public class FindSameChar {  
      
    public  char findSameChar(String str){    
        int length = str.length();    
        for(int i = 0;i<length;i++)    
            for(int j=i+1;j<length;j++)    
            {    
                if(str.charAt(i)==str.charAt(j)){    
                    return str.charAt(i);    
                }    
            }  
        return 0;  
    }    
        
    public  char findSameMap(String str){    
        HashMap<Character, Integer> map = new HashMap<Character, Integer>();    
        for(int i=0;i<str.length();i++){    
            if(map.containsKey(str.charAt(i))){  
                return str.charAt(i);  
            }else    
            {    
                map.put(Character.valueOf(str.charAt(i)), Integer.valueOf(1));    
            }    
        }  
        return 0;  
    }  
      
    public  char findSameBitSet(String str) {  
        BitSet set = new BitSet(255);  
        for (int i = 0; i < str.length(); i++) {  
            if (set.get(str.charAt(i))) {  
                return str.charAt(i);  
            } else {  
                set.set(str.charAt(i), true);  
            }  
        }  
        return 0;  
    }  
      
    private static final Pattern p = Pattern.compile("(\\w).*\\1");    
      
    public  String findSameRegEx(String s) {    
        Matcher m = p.matcher(s);    
        if (m.find()) {    
            return m.group(1);    
        } else {    
            return null;    
        }    
    }   
      
    private static final long TIMES = 100*1000*1000;  
      
    public static void main(String[] args) {  
        char result = 0;  
        FindSameChar test = new FindSameChar();
        long t = System.currentTimeMillis();  
        for (long i = 0; i < TIMES; i++) {  
            result = test.findSameChar("abcdefghijklmnopqrstbab");  
        }  
        t = System.currentTimeMillis() - t;  
        System.out.println("findSameChar : Result " + result + " in " + t);  
          
        result = 0;  
        t = System.currentTimeMillis();  
        for (long i = 0; i < TIMES; i++) {  
            result = test.findSameMap("abcdefghijklmnopqrstbab");  
        }  
        t = System.currentTimeMillis() - t;  
        System.out.println("findSameMap : Result " + result + " in " + t);  
 
        result = 0;  
        t = System.currentTimeMillis();  
        for (long i = 0; i < TIMES; i++) {  
            result = test.findSameBitSet("abcdefghijklmnopqrstbab");  
        }  
        t = System.currentTimeMillis() - t;  
        System.out.println("findSameBitSet : Result " + result + " in " + t);  
          
        String strResult = null;  
        t = System.currentTimeMillis();  
        for (long i = 0; i < TIMES; i++) {  
            strResult = test.findSameRegEx("abcdefghijklmnopqrstbab");  
        }  
        t = System.currentTimeMillis() - t;  
        System.out.println("findSameRegEx : Result " + strResult + " in " + t);  
    }  
}   
/**
 * 运行结果，原以为findSameMap最快，哈哈，最终最简单的总是最快的
    findSameChar : Result a in 10547
    findSameMap : Result b in 246000
    findSameBitSet : Result b in 76328
    findSameRegEx : Result a in 127187
*/