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].

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        int size = nums.size();
        vector<int> result;
        map<int, int> lookup;
        for(int i = 0; i < size; i++) {
            int value = target - nums[i];
            if (lookup.count(value)) {
                result.push_back(lookup[value]);
                result.push_back(i);
                return result;
            } else {
                lookup.insert(pair<int, int>(nums[i], i));
            }
        }
    }
};

 

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        map = {}
        res = []
        for i in range(nums.__len__()):
            map[target - nums[i]] = i
        for i in range(nums.__len__()):
            if (map.get(nums[i]) and (map.get(nums[i]) != i)):
                res.append(i)
                res.append(map.get(nums[i]))
                return res