LeetCode3. 无重复字符的最长子串

class Solution {
    public int lengthOfLongestSubstring(String s) {
        if(s.length() == 0)
            return 0;
        Map<Character,Integer> pos = new HashMap<Character,Integer>();
        int[] pre = new int[s.length()];
        char[] str = s.toCharArray();
        for(int i = 0;i < s.length();i++) {
            Integer lastPos = pos.get(str[i]);
            if(lastPos == null) {
                pre[i] = i == 0 ? 1 : pre[i - 1] + 1;
                pos.put(str[i],i);
            } else {
                int aPos = lastPos + 1;
                int repeatLen = pre[i - 1];
                int bPos = i - repeatLen;
                if(aPos >= bPos)
                    pre[i] = i - aPos + 1;
                else
                    pre[i] = i - bPos + 1;
                pos.put(str[i],i);
            }
        }
        int max = pre[0];
        for(int i : pre)
            max = Math.max(max,i);
        return max;
    }
}