3. Longest Substring Without Repeating Characters

Given a string s, find the length of the longest

substring

without repeating characters.

Example 1:

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

Example 2:

Input: s = "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: s = "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.

Constraints:

• 0 <= s.length <= 5 * 104
• s consists of English letters, digits, symbols and spaces.

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int result=0;
        int left=0;
        unordered_set<char>window;
        for(int right=0;right<s.length();right++){
            char c=s[right];
            while(window.count(c)){
                window.erase(s[left++]);
            }
            window.insert(c);
            result=max(result,right-left+1);
        }
        return result;
    }
};

注意：

        1.同样的，left表示起始位置，right表示终止位置，均从零开始，用result来记录最后的最小长度。

        2.创建一个哈希表Window，用来记录不重复的字符串

        3.注意while循环，当Window里面已经有过c的时候，一直将Window的left++的元素删除，注意，left同时也会++，以此来保证最后得到的字符串长度是最小的。

        4.result是result和right-left+1两者中的较大值