题目:https://leetcode-cn.com/problems/two-sum/
方法一:
class Solution:
def twoSum(self, nums: List[int], target: int) -> List[int]:
answer=[]
for i in range(len(nums)):
for j in range(i+1,len(nums)):
sum=nums[i]+nums[j]
if sum==target:
answer.append(i)
answer.append(j)
break;
return answer
时间复杂度太大
方法二:
先建立一个字典,遍历list,求target与当前值得差值a。如果nums[i]不在字典中,则将(a:i)加入字典,否则输出。
字典存放每个数与target的差值和该数下标
其他语言可以采用哈希表思想,如map
class Solution:
def twoSum(self, nums: List[int], target: int) -> List[int]:
dic={}
for i in range(len(nums)):
a=target-nums[i]
if nums[i] in dic:
return dic[nums[i]],i
else:
dic[a]=i