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].
解题思路：
采用一个字典，key是list里的值，value是值对应的在list中的index。依次在list循环，如果期望值和list中某值的差在数组中，就返回对应的两个index。如果不存在，就放入字典中，继续循环。
具体代码
#!/usr/bin/env python
# -*- coding: UTF-8 -*-
class Solution(object):
def twoSum(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: List[int]
"""
dict = {}
for i in xrange(len(nums)):
expected = target - nums[i]
# print i, expected, dict
if expected in dict.keys():
return [dict[expected], i]
dict[nums[i]] = i
if __name__ == "__main__":
sol = Solution()
nums = [3, 2, 4]
print sol.twoSum(nums, 6)
nums = [2, 11, 7, 15]
print sol.twoSum(nums, 9)
nums = [3, 6, 8, 9, 10, 21, 12]
print sol.twoSum(nums, 18)
