給定 nums = [2, 7, 11, 15], target = 9
因為 nums[0] + nums[1] = 2 + 7 = 9，所以返回 [0, 1]

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        if len(nums) < 2:
            return []

        iLen = len(nums)
        for i in range(iLen):
            for j in range(i + 1, iLen):
                if nums[i] + nums[j] == target:
                    return [i, j]
        return []

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        if len(nums) < 2:
            return []

        iLen = len(nums)
        hashDict = {}
        for i in range(iLen):
            find = target - nums[i]
            if find in hashDict:
                return [hashDict[find], i]
            else:
                hashDict[nums[i]] = i
        return []