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].

My solution:

class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        for i in range(len(nums)):
            if target - nums[i] in nums:
                if i != nums.index(target - nums[i]):
                    return [i, nums.index(target - nums[i])]

        return None

Good solution:

class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        dist = {}

        for i in range(len(nums)):
            if target - nums[i] in dist:
                return [dist[target - nums[i]], i]
            dist[nums[i]] = i

        return None

Instead of using dict(), use {}.

It's good for runtime.