3. Longest Substring Without Repeating Characters

https://leetcode.com/problems/longest-substring-without-repeating-characters/

Problem

Given a string s, find the length of the 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

Constraints:

• 0 <= s.length <= 5 * 104

• s consists of English letters, digits, symbols and spaces.

Solution

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        if (s.empty()) return 0;
        unordered_map<char, int> indice;
        indice.reserve(s.size());
        int max_len = 0;
        int j = 0;
        for (int i = 0; i < s.size(); ++i) {
            if (indice.find(s[i]) != indice.end()) j = max(j, indice[s[i]] + 1);
            indice[s[i]] = i;
            max_len = max(max_len, i - j + 1);
        }
        return max_len;
    }
};

• #hash