描述
给一个整数数组，找到两个数使得他们的和等于一个给定的数 target。
你需要实现的函数twoSum需要返回这两个数的下标, 并且第一个下标小于第二个下标。注意这里下标的范围是 0 到 n-1。
你可以假设只有一组答案。
您在真实的面试中是否遇到过这个题？ 是
样例
给出 numbers = [2, 7, 11, 15], target = 9, 返回 [0, 1].
挑战
Either of the following solutions are acceptable:
- O(n) Space, O(nlogn) Time
- O(n) Space, O(n) Time
两个思路，一个是使用hash表映射，另一个是直接两个循环直接比较
class Solution:
"""
@param numbers: An array of Integer
@param target: target = numbers[index1] + numbers[index2]
@return: [index1, index2] (index1 < index2)
"""
'''
#hash
def twoSum(self, numbers, target):
# write your code here
hash = {}
for i, num in enumerate(numbers):
if target - num in hash:
return [hash[target-num], i]
hash[num] = i
return [-1, -1]
'''
'''
def twoSum(self, numbers, target):
# write your code here
for i in range(len(numbers)):
for j in range(i):
if numbers[i] + numbers[j] == target:
return [j, i]
'''
def twoSum(self, numbers, target):
# write your code here
for i in range(len(numbers)):
for j in range(len(numbers)-1, i, -1):
if numbers[i] + numbers[j] == target:
return [i, j]