Leetcode刷题104-3. 无重复字符的最长子串(C++详细解法！！！)

Come from : [https://leetcode-cn.com/problems/longest-substring-without-repeating-characters/]

1.Question

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.

2.Answer

medium 类型题目。（稍后补充思路。。。睡觉去了）。
时间复杂度O(n)，空间复杂度O(n)，使用哈希表，滑动窗口。

算法思路见下图：

AC代码如下：

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int begin = 0;           //窗口的头指针
        int result = 0;
        string word = "";
        int char_map[128] = {0};
        
        for(int i = 0; i < s.length(); ++i)
        {
            char_map[s[i]]++;
            if(char_map[s[i]] == 1)  //等于1  表示word中 没有出现该字符
            {
                word += s[i];
                if(result < word.length())
                {
                    result = word.length();
                }
            }
            else
            {   //将重复的 s[i]删去
                while(begin < i && char_map[s[i]] > 1)
                {
                    --char_map[s[begin]];
                    ++begin;
                }
                word = "";
                for(int j = begin; j <= i; ++j) //重新更新 word
                {
                    word += s[j];
                }
            }
        }
        return result;
    }
};

3.大神解答

速度排名第一，明天仔细看下。

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int  size,i=0,j,k,max=0;
        size = s.size();
        for(j = 0;j<size;j++){
            for(k = i;k<j;k++)
                if(s[k]==s[j]){
                    i = k+1;
                    break;
                }
            if(j-i+1 > max)
                max = j-i+1;
        }
        return max;
    }
};

4.我的收获

字符串与哈希表的集合。
fighting。。。

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2019/6/19 胡云层 于南京 104