leetcode 3. Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without repeating characters.

Examples:

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.

解：需要采用在线处理的方法，同时还要记录没哟个字符是否读取过，这可以使用map，其实看他人的solution也可以vector容器，都是同一种思路。
代码：class Solution {
public:
int lengthOfLongestSubstring(string s) {
map<int, int> hashMap;
int len = s.length();
int head = -1;
int maxlen = 0;
for(int i = 0; i < len; i++){
hashMap[s[i]] = -1;
}
for(int i = 0; i < len; i++){
if(hashMap[s[i]] > head){
head = hashMap[s[i]];
}
hashMap[s[i]] = i;
maxlen = max(maxlen, i - head);
}
return maxlen;
}
};