3.Longest Substring Without Repeating Characters

for example:

Given 

"abcabcbb"

, the answer is 

"abc"

,
which the length is 3.

Given 

"bbbbb"

, the answer is 

"b"

,
with the length of 1.

Given 

"pwwkew"

, the answer is 

"wke"

,
with the length of 3. Note that the answer must be a substring, 

"pwke"

 is
a subsequence and not a substring.

code:

time complexity o（2n）

think:

clear_thought is the key to clear_code

class Solution {
public:
int lengthOfLongestSubstring(string str) {

int result = 0;
int i = 0;
int j = 0;
int len = str.length();

set<char> s;
while(i<len && j < len){
if(s.count(str[j])==0){
s.insert(str[j]);
j++;
result = (j-i)>result?(j-i):result;
}else{
s.erase(str[i]);
i++;
}
}

return result;
}
};