3. Longest Substring Without Repeating Characters

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Question:

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.

Example 4:

Input: s = ""
Output: 0

Solution 1:

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;
    }
};

Solution 2: 思路类似。

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
		int maxLen = 0, start = -1;
		unordered_map <char, int> hashMap;
		for(int i = 0; i < s.length(); i++)
		{
			if (hashMap.find(s[i]) != hashMap.end())
			{
				start = hashMap[s[i]] > start? hashMap[s[i]]:start;
			}
			hashMap[s[i]] = i;
			maxLen = max(maxLen, i - start);
		}
        return maxLen;
    }
};

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