class Solution {
public int lengthOfLongestSubstring(String s) {
int len_s = s.length();
if(len_s == 0){
return 0;
}
int head = 0;
int tail = 1;
int res = 1;
while(tail < len_s){
int find = s.substring(head,tail).indexOf(s.charAt(tail));
if(find >= 0){
head = head + find + 1;
}
tail += 1;
if(tail - head > res){
res = tail - head;
}
}
return res;
}
}
