给定一个整数数组 nums和一个整数目标值 target，请你在该数组中找出 和为目标值 的那两个整数，并返回它们的数组下标。
你可以假设每种输入只会对应一个答案。但是，数组中同一个元素在答案里不能重复出现。
你可以按任意顺序返回答案。
示例 1：
输入：nums = [2,7,11,15], target = 9
输出：[0,1]
解释：因为 nums[0] + nums[1] == 9 ，返回 [0, 1] 。
class TwoSum:
"""
nums: [int]
target: int
return: two ele's index, [int]
"""
def __init__(self, nums, target):
self.nums = nums
self.target = target
def demo_On2(self):
"""
O(n^2)
:return:
"""
for i in range(len(self.nums)):
for j in range(i+1, len(self.nums)):
if self.nums[i] + self.nums[j] == self.target:
return [i, j]
return []
def demo_Onlogn(self):
"""
O(nlogn)
:return:
"""
# sorted_id >>> list consist of every ele's index in the nums
sorted_id = sorted(range(len(self.nums)), key= lambda k:self.nums[k])
print(sorted_id)
head = 0
tail = len(self.nums) - 1
sum_res = self.nums[sorted_id[head]] + self.nums[sorted_id[tail]]
while sum_res != target:
if sum_res > target:
tail -= 1
elif sum_res < target:
head += 1
sum_res = self.nums[sorted_id[head]] + self.nums[sorted_id[tail]]
return [sorted_id[head], sorted_id[tail]]
def demo_On(self):
"""
O(n)
:return:
"""
dict_ = {}
# enumerate >>> generator obj
for index, num in enumerate(nums):
other_num = self.target - num
if other_num in dict_:
return [dict_[other_num], index]
# key >>> num, index >>> value
dict_[num] = index
return None
if __name__ == "__main__":
nums = [1, 3, 8, 2, 8, 5]
target = 16
twoSum = TwoSum(nums, target)
res = twoSum.demo_On()
print(res)
来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/two-sum
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