Leetcode 3. 无重复字符的最长子串

class Solution {
public:
int lengthOfLongestSubstring(string s) {
int beg = 0;
int result = 0;
string word = "";
int char_map[128] = {0};
for(int i=0; i<s.size(); ++i)
{
char_map[s[i]]++;
if(char_map[s[i]] == 1)// 没有出现过
{
word+=s[i];
if(result < word.size())
result = word.size();
}
else//已经出现过了
{
while(beg <i && char_map[s[i]] > 1)
{
char_map[s[beg]]--;
beg++;
}
word = "";
for(int j=beg; j<=i ;++j)
word+=s[j];
}
}
return result;
}
};