[LeetCode][Python]1. TWO SUM

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)