3 Longest Sub-string without repeating character

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.

Using hashmap to track the repeating characters and the index of it:

Method 1:

By using HashMap, we can keep track of a mapping of each character with its index. Also, through checking if(noDupMap.containsKey(word)), we can directly skip the repeating character. At the same time, move the pointer to the position one after the earliest index of the repeating character. The search costs O(1), while the whole traverse causes O(N).

Time compacity: O(size) - index i will iterate input.size times Space compacity: O(size) - the size is the length of the noDupMap.