3-Longest Substring Without Repeating Character

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.

题意：找到字符串中的一个子串，该子串是无重复的最长子串。

思路：最大滑窗算法

           左指针指向不重复子串的第一个字符，右指针指向要检测的字符。

           如果要检测的字符在【左指针，右指针），滑窗左指针应该移动到和检测字符重复字符的右边一位。

           不在那个范围，证明左指针不需要更新，因为检测字符和左侧的字符都没有重复

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           此时，滑窗不存在重复字符，所有右指针右移，继续指向下一个要检测的字符

说明：每次检测完一个字符后，才能将这个字符对应到哈希表。

class Solution {
public:
    
    int lengthOfLongestSubstring(string s) {
        
        int len = s.length();
        
        if( len == 0 )
            return 0;
        if( len == 1 )
            return 1;
        
        int ret = 1;
        int left = 0, right = 1; 
        
        map<char, int> m;
        
        m[s[left]] = 0;
        
        while( right < len )
        {
            if( m.find(s[right]) != m.end() && (m[s[right]] >= left) )
            {
                left = m[s[right]] + 1;
            }
            
            m[s[right]] = right++;
          
            ret = (ret > (right-left)) ? ret : (right-left);
        }
        return ret;
    }
};