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.
思路：遍历字符串找最长不重复字串，用hash表记录下已有的字符，用begin来记录开始计数的位置。如果下一个字符在hash表中已经记录了，就修改begin和hash的值来继续下一次查找
1 class Solution { 2 public: 3 int lengthOfLongestSubstring(string s) { 4 int maxLength=0;//记录下最长的不重复字串的长度 5 int length=0; 6 int begin=0;//记录下开始计算长度的位置 7 short hash[128];//哈希表，ASCII码，最多不超过128个字符 8 memset(hash, 0, sizeof(hash)); 9 for(int idx=0; idx<s.size(); ++idx) 10 { 11 12 int key=s[idx]-‘\0‘; 13 if(hash[key]==0) 14 { 15 hash[key]=1; 16 ++length; 17 if(length>maxLength)maxLength=length; 18 if(maxLength==128)return 128;//如果最大长度达到128，立即返回，无须再比较下去 19 }else{ 20 while(s[begin]!=s[idx]) 21 { 22 int key=s[begin]-‘\0‘; 23 hash[key]=0; 24 --length; 25 ++begin; 26 } 27 ++begin; 28 } 29 } 30 return maxLength; 31 } 32 };