求一个字符串的最长无重复字母的连续子串

如字符串“abacdabefac”， 则其最长无重复字母的连续子串是：“cdabef”

java实现如下：

package com.test;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

public class FindSubString {

public static String findSubStr(String str) {
Map<Character, Integer> indexMap = new HashMap<Character, Integer>();
if (null == str || str.isEmpty()) {
return str;
}
char[] tmpList = new char[str.length()];
String result = null;
int tmpLength = 0;
for (int i = 0; i < str.length();) {
char c = str.charAt(i);
if (indexMap.get(c) == null) {
indexMap.put(c, i);
tmpList[tmpLength++] = c;
i++;
} else {
if (null == result || result.length() < tmpLength) {
result = new String(tmpList, 0, tmpLength);
}
tmpLength = 0;
i = indexMap.get(c) + 1;
indexMap.clear();
}
}
if (null == result || result.length() < tmpLength) {
result = new String(tmpList, 0, tmpLength);
}
return result;
}

public static String findSubStrImprove1(String str) {
Map<Character, Integer> indexMap = new HashMap<Character, Integer>();
if (null == str || str.isEmpty()) {
return str;
}
int preStart = 0;
int preEnd = 0;
int start = 0;
int end = 0;
for (int i = 0; i < str.length();) {
char c = str.charAt(i);
if (indexMap.get(c) == null) {
indexMap.put(c, i);
} else {
if ((preEnd - preStart) < (end - start)) {
preStart = start;
preEnd = end;
}

start = indexMap.get(c) + 1;
for(int j = 0; j < start; j++){
indexMap.remove(str.charAt(j));
}
/*
System.out.print("counting " + i + " th char:" + c + ", appeared before, current longest: "
+ str.substring(preStart, preEnd) + ",start = "+ preStart+",end = " +preEnd + "\t");
System.out.println("now start = " + start);*/
indexMap.put(c, i);
}
i++;
end++;
}
if ((preEnd - preStart) >= (end - start)) {
start = preStart;
end = preEnd;
}
return str.substring(start, end);
}

public static void main(String[] args) {
String str = "abacdabefac";//output:cdabef
System.out.println(findSubStr(str));
System.out.println(findSubStrImprove1(str));
str = "afhjufamtbdehtskoitdc";//output:hjufamtbde
System.out.println(findSubStr(str));
System.out.println(findSubStrImprove1(str));
str = "ababcdefgcdabmn";//output:efgcdabmn
System.out.println(findSubStr(str));
System.out.println(findSubStrImprove1(str));
}

}