2019-07-03

删除链表倒数第N个节点

class Solution:
    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
        
        p = q = head
        for _ in range(n):
            q = q.next
        if not q:
            return p.next
        while q.next:
            p, q = p.next, q.next
        p.next = p.next.next
        return head

最长回文子串

class Solution:
    def longestPalindrome(self, s: str) -> str:
        res = ""
        for i in range(len(s)):
            tmp = self.helper(s, i, i)
            if len(tmp) > len(res):
                res = tmp
                
            tmp = self.helper(s, i, i+1)
            if len(tmp) > len(res):
                res = tmp
        return res
    
    def helper(self, s, l, r):
        while l>=0 and r < len(s) and s[l]==s[r]:
            l -= 1
            r += 1
        return s[l+1:r]

无重复字符的最长子串

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        left = right = res = 0
        char = dict()
        for right in range(len(s)):
            if s[right] in char:
                left = max(left, char[s[right]] + 1)
            char[s[right]] = right
            res = max(res, right - left + 1)
        return res