【LeetCode刷题系列

题目：

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. 

Example 2:

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

Example 3:

Input: "pwwkew"
Output: 3
Explanation: 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.

代码(C++实现)：

class Solution {
public:
    int lengthOfLongestSubstring(string s) 
    {
        // 定义一个map用来存放整个字符串s
        unordered_map<char, int> unmap;
        
        // tempLength记录每次扫描位置开始的一次统计的最长字符串的长度
        int tempLength = 0;
        // 众多tempLength中的最大值
        int maxLength = 0;
        
        // 第一层循环：分别以s中的每个字符为基准，进行遍历
        for (int j = 0; j < s.size(); j++)
        {
            // 第二层循环：以当前第一层循环中当前的字符为基准，进行遍历，统计以此字符为基准的tempLength
            for (int i = j; i < s.size(); i++)
            {
                // 是否tempLength继续增加的条件是，map中没有出现过当前指向的字符
                if (unmap.count(s[i]) == 0)                
                {
                    pair<char, int> myshopping(s[i], i);
                    // 如果当前的map中无此字符，将当前字符插入到map中
                    unmap.insert(myshopping);
                    tempLength++;
                    maxLength = maxLength > tempLength ? maxLength : tempLength;
                }
                // 当前字符已经在map中了，直接break，并将本次使用的map进行清除操作
                else
                {
                    
                    tempLength = 0;
                    unmap.clear();
                    break;
                }

            }
        }
    
        return maxLength;
        }
};