3. Longest Substring Without Rep

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

Example 1:

Input: "abcabcbb"
Output: 3 
Explanation: The answer is "abc", with the length of 3. 

寻找字符串没有重复字符的最长字串，可以用一个start指针指向字串的开始，用一个字典存储所有遍历过的字符的下标。遍历字符串的时候将当前的字串的长度和记录的字串的长度比较，获得最优的字串的长度。

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int maxLen = 0;
        int beginIndex = 0;
        map<char, int> charIndex;
        int len = s.size();
        for(int i=0; i < len; i++){
            if(charIndex.find(s[i]) == charIndex.end() || charIndex[s[i]] < beginIndex){
                charIndex[s[i]] = i;
                maxLen = max(maxLen, i-beginIndex+1);
            }
            else{
                beginIndex = charIndex[s[i]]+1;
                charIndex[s[i]] = i;
            }
        }
        return maxLen;
    }
};