题目:
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].
Answer:
1. 简单的递归(5446ms)
class Solution(object):
def twoSum(self, nums, target):
for i in range(0, len(nums) - 1):
for j in range(i + 1, len(nums)):
if nums[i] + nums[j] == target:
return [i, j]
return [-1, -1]
2. 利用list的index特性(1284ms)
class Solution(object):
def twoSum(self, nums, target):
for i in range(len(nums)):
if target - nums[i] in nums:
j = nums.index(target - nums[i])
if i != j:
return [i, nums.index(target - nums[i])]
return [-1, -1]
其中j为判断是否为同一index
3. 利用dict(36ms)
class Solution(object):
def twoSum(self, nums, target):
d = {}
for i in range(len(nums)):
if nums[i] not in d:
d[target - nums[i]] = i
else:
return [d[nums[i]], i]
return [-1, -1]