力扣-1两数之和2两数相加-2024/8/3

1、两数之和

解法一 暴力法（2个for循环）

class Solution:def twoSum(self, nums: List[int], target: int) -> List[int]:for ii in range(len(nums)):for jj in range(ii+1, len(nums)):if nums[ii]+nums[jj] == target:return [ii,jj]

解法二 哈希表法

class Solution:def twoSum(self, nums: List[int], target: int) -> List[int]:hash = {}for ii, num in enumerate(nums):if target-num in hash:return [hash[target-num],ii]hash[num] = ii

哈希表[key]=value
key是数值
value是索引值
便历索引，数值用枚举enumerate；
2、两数相加

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:# 初始化链表ListNode()表示链表，head表示静止表头，tree表示动态指针；val是相加后/10的余数，tmp是商；head = tree = ListNode()val = tmp = 0# 当三者有一个不为空时，继续循环while tmp or l1 or l2:val = tmpif l1:val = l1.val + vall1 = l1.nextif l2:val = l2.val + vall2 = l2.nexttmp = val // 10val = val % 10tree.next = ListNode(val)tree = tree.nextreturn head.next