3. Longest Substring Without Repeating Characters

1. Description

Given a string s, find the length of the longest substring without duplicate characters.

2. Example

Example 1

Input: s = “abcabcbb”
Output: 3
Explanation: The answer is “abc”, with the length of 3. Note that “bca” and “cab” are also correct answers.

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.

3. Constraints

• 0 <= s.length <= 5 * $10^4$
• s consists of English letters, digits, symbols and spaces.

4. Solutions

Sliding Window

n = str.size()
Time complexity: O(n)
Space complexity: O(1)

class Solution {
public:
    int lengthOfLongestSubstring(const string &str) {
        array<int, 128> prev_index;
        prev_index.fill(-1);

        const int n = str.size();
        int max_length = 0;
        for (int left = 0, right = 0; right < n; ++right) {
            left = max(prev_index[str[right]] + 1, left);
            max_length = max(right - left + 1, max_length);
            prev_index[str[right]] = right;
        }

        return max_length;
    }
};