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two_sum.py
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41 lines (32 loc) · 1.35 KB
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# Given an array of integers, return indices of the two numbers such that they add up to a specific target.
# You may assume that each input would have exactly one solution, and you may not use the same element twice.
# Example:
# Given nums = [2, 7, 11, 15], target = 9,
# Because nums[0] + nums[1] = 2 + 7 = 9,
# return [0, 1].
# Solution 1: O(n^2) in time
class Solution:
def twoSum(self, nums: List[int], target: int) -> List[int]:
for i in range(len(nums)):
for j in range(i+1,len(nums)):
if (nums[i] + nums[j]) == target:
return [i, j]
# Solution 2: O(n) in time
class Solution:
def twoSum(self, nums: List[int], target: int) -> List[int]:
hash_map = {}
for i in range(len(nums)):
hash_map[nums[i]] = i
for i in range(len(nums)):
complement = target - nums[i]
if (complement in hash_map and hash_map[complement] != i):
return [i, hash_map[complement]]
# Solution 3: O(n) in time
class Solution:
def twoSum(self, nums: List[int], target: int) -> List[int]:
hash_map = {}
for i in range(len(nums)):
complement = target - nums[i]
if (complement in hash_map and hash_map[complement] != i):
return [hash_map[complement], i]
hash_map[nums[i]] = i