Given an array of integers, find two numbers such that they add up to a specific target number.
The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.
You may assume that each input would have exactly one solution.
Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2
Code:
class Solution(object):
def twoSum(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: List[int]
"""
dict = {}
for idx, vlu in enumerate(nums):
idx2 = dict.get(target - vlu, -1)
if idx2 < 0:
dict[vlu] = idx
else:
return [idx2+1, idx+1]
Idea:
O(N) space. O(N) time. Read my another post on 3Sum, which sorts array in place in O(nlogn) time but costs no additional space. (3Sum algorithm takes O(N^2) overall)
UPDATE (2016/2/13):
The return format had been changed to zero-based indices. Please read the above updated description carefully.