3. 无重复字符的最长子串

leetcode的题解：
https://leetcode-cn.com/problems/longest-substring-without-repeating-characters/solution/wu-zhong-fu-zi-fu-de-zui-chang-zi-chuan-by-leetcod/

java版：

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length(), ans = 0;
        Map<Character, Integer> map = new HashMap<>(); // current index of character
        // try to extend the range [i, j]
        for (int j = 0, i = 0; j < n; j++) {
            if (map.containsKey(s.charAt(j))) {
                i = Math.max(map.get(s.charAt(j)), i);
            }
            ans = Math.max(ans, j - i + 1);
            map.put(s.charAt(j), j + 1); 	//注：重复key会覆盖value值 
            //System.out.println(map);
        }
        return ans;
    }
}

 map.put(s.charAt(j), j + 1); 

上面这里存的是j+1而不是j，方便i更新值

i = Math.max(map.get(s.charAt(j)), i); //取大的防止i左移

可以改成这样：

改成C++:

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

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        map<char,int> mymap;
        int ans = 0;
        for(int i = 0, j = 0; j < s.size(); j++)
        {
            i = max(mymap[s[j]], i);	//如果mymap里没s[j]这个key,mymap[s[j]] = 0
            ans = max(ans, j - i + 1);
            mymap[s[j]] = j + 1;
        }
        return ans;
    }
};

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        vector<int>mymap(256,-1);
        int left = -1;
        int res = 0;
        int len = s.size();
        for(int i = 0; i < len; i++)
        {
            left = max(mymap[s[i]], left);
            mymap[s[i]] = i;
            res = max(res, i - left);
        }
        return res;
    }
};

参考：
leetcode
https://leetcode-cn.com/problems/longest-substring-without-repeating-characters/solution/wu-zhong-fu-zi-fu-de-zui-chang-zi-chuan-by-leetcod/

来源：CSDN

作者：曾庆发

链接：https://blog.csdn.net/qq_40691051/article/details/103645390