3. Longest Substring Without Repeating Characters

最新推荐文章于 2025-05-18 01:04:12 发布

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本文探讨了如何找出给定字符串中最长的无重复字符子串，并提供了两种不同的C++实现方案。通过使用哈希表和双指针技巧，有效地解决了这一经典问题。

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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.

做了蛮久。调试了好多次。 hash table two pointers ~ 写的有点复杂。

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        if(s.empty()) return 0;
        int max = 0,ans = 1;
        unordered_map<char, int> mp;
        mp[s[0]] = 1;
        int pre = 0;
        int cur = 0;
        for(int i = 1; i < s.size(); ++i){
            if(mp[s[i]] == 0){
                cur = i;
                mp[s[i]] = i+1;
            }
            else{
                    cur = i;
                    pre = (mp[s[i]] > pre) ? mp[s[i]] : pre;
                    mp[s[i]] = i + 1;
          }
            
            max = cur - pre + 1;
            if(max > ans) ans = max;
        
        }
        return ans;
    }
        
};

better!

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        vector<int> dict(256, -1);
        int maxLen = 0, start = -1;
        for (int i = 0; i != s.length(); i++) {
            if (dict[s[i]] > start)
                start = dict[s[i]];
            dict[s[i]] = i;
            maxLen = max(maxLen, i - start);
        }
        return maxLen;
    }
        
};