2 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.

Example:

nums = [2, 7, 11, 15] target = 9

returns

[0, 1]

because nums[0] + nums[1] = 2 + 7 = 9.

UPDATE (2016/2/13): The return format had been changed to zero-based indices. Please read the above updated description carefully.

Python

def twoSum(nums, target):
    """
    :type nums: List[int]
    :type target: int
    :rtype: List[int]
    """
    memo = {}
    for i in range(len(nums)):
        compliment = memo.get(nums[i])
        if compliment != None:
            return [compliment, i]
        memo[target-nums[i]] = i

Javascript

// @flow
const twoSum = (nums: ?number[], target: number) => {
  var memo: {
    [compliment: number]: number
  } = {}
  if (nums == null) return null;
  for (var i = 0; i < nums.length; i++) {
    if (memo[nums[i]] != null) {
      return [memo[nums[i]], i]
    }
    memo[target - nums[i]] = i
  }
}