#https://leetcode.com/problems/two-sum/ """ when we iterate through the nums we don't know if the counter part exist so we store the counter part we want in the 'wanted' with the index now so inside the wanted is {the_counter_part_we_want:index_now} [0] later on if we found the num is in 'wanted' we return the index_now and the index_now we previously stored in the 'wanted' [1] """ class Solution(object): def twoSum(self, nums, target): wanted = {} for i in xrange(len(nums)): n = nums[i] if n in wanted: #[1] return [wanted[n], i] else: wanted[target-n] = i #[0] return []