Longest Substring Without Repeating Characters

从左往右扫描，当遇到重复字母时，以上一个重复字母的index +1，作为新的搜索起始位置。

可以减少时间， 但时间复杂度没有变O(n²)

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(s == null)
            return 0;
        char[] mychar = s.toCharArray();
        HashMap<Character, Integer> table = new HashMap<Character, Integer>();
        int result = 0;
        for(int i=0; i<mychar.length; i++)
        {
            if(table.containsKey(mychar[i]))
                {
                    result = table.size() > result? table.size():result;
                    i = table.get(mychar[i]);
                    table.clear();
                }
            else
                table.put(mychar[i], i);
        }
        result = table.size() > result? table.size():result;
        return result;
    }
}