## 3. No repeating characters longest substring 141. The circular linked list 171. Excel table column list element number 203. remove

#### 3. No repeating characters longest substring

Given a string, you find out which does not contain a sub-length of the longest string of repeated characters.

Example 1:

Input: "abcabcbb"
Output: 3
Explanation: Because the longest substring of characters without repetition is "abc", so its length is 3.
Example 2:

Input: "bbbbb"
Output: 1
Explanation: Because the longest substring is repeated characters without "b", so that its length is 1.
Example 3:

Input: "pwwkew"
Output: 3
Explanation: Because the longest sub-string is repeated characters without "wke", so its length is 3.
Please note that your answer must be a substring of length, "pwke" is a sub-sequence, not a substring.

Source: stay button (LeetCode)

`class Solution:    def lengthOfLongestSubstring(self, s: str):        st = {}        i, ans = 0, 0        for j in range(len(s)):            if s[j] in st:                i = max(st[s[j],i])            ans = max(ans, j-i+1)            st[s[j]] = j + 1        return ans`

#### 141. The circular linked list

Given a list, the list is determined whether a ring.

To show the list given ring, we integer pos connected to the end of the list to represent the position of the list (index starts from 0). If pos is -1, the ring is not on this list.

Example 1:

Input: head = [3,2,0, -4] , pos = 1
Output: true
explanation: the list has a ring tail portion connected to a second node.

Example 2:

Input: head = [1,2], pos = 0
Output: true
explanation: the list has a ring, which is connected to the tail of the first node.

Example 3:

Input: head = [1], pos = -1
Output: false
interpretation: the list does not ring.

You can use O (1) (ie, constant) memory to solve this problem?

Source: stay button (LeetCode)

`class ListNode(object):    def __init__(self):        self.val = x        self.next = Noneclass Solution:    def hasCycle(self, head):        fast, slow = head, head        while fast and fast.next:            fast, slow = fast.next.next, slow.next            if fast == slow:                return True        return False`

#### 171. Excel table column number

Given a column name of the Excel spreadsheet returns the corresponding column number.

E.g,

A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27
AB -> 28
...

Input: "A"
Output: 1
Example 2:

Input: "AB"
Output: 28
Example 3:

Enter: "ZY"
output: 701

Source: stay button (LeetCode)

`class Solution(object):    def titleToNumber(self, s):        """        :type s: str        :rtype: int        """        result = 0        for i in range(len(s)):            result *=26            result += ord(s[i]) - ord('A') + 1        return result`

#### 203. remove list elements

Delete the list is equal to a given value  val  all nodes.

Example:

```Input: 1-> 2-> 6-> 3-> 4-> 5->. 6, Val =. 6
Output: 1-> 2-> 3-> 4-> 5```
`# 203 移出链表元素# Definition for singly-linked list.class ListNode(object):    def __init__(self, x):        self.val = x        self.next = Noneclass Solution(object):    def removeElements(self, head, val):        """        :type head: ListNode        :type val: int        :rtype: ListNode        """        dummy = ListNode(0)        dummy.next = head        prev, curr = dummy, dummy.next        while curr:            if curr.val == val:                prev.next = curr.next            else:                prev = curr            curr = curr.next        return dummy.next`

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