[LeetCode] #3. Longest Substring Without Repeating Characters

[Medium[Question]:

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.

My Solution[C++]:

[Ideas]: 先講重點，取出每個字元與前一個重複字元的距離，取max !

先建立一個全為-1的vector，長度為256( ASCII 表共能表示 256 个字符)，從最左邊起始位置找到最右邊，分為三個步驟。

step1.若此char上次有出現過，把Ptr_Start 更新到上次出現的位置

step2.把char對應到vector上的數字，update成目前指到的位置

step3.與上次的答案比大小，這次的答案為每個此字元到上次出現的位置距離