001 Two Sum


Problem

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

1
2
3
4
Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

Python

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
class Solution(object):
def twoSum(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: List[int]
"""
lookup = {}
for i, num in enumerate(nums):
if target - num in lookup:
return [lookup[target - num], i]
lookup[num] = i

def twoSum2(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: List[int]
"""
k = 0
for i in nums:
j = target - i
k += 1
tmp_nums = nums[k:]
if j in tmp_nums:
return [k - 1, tmp_nums.index(j) + k]


if __name__ == '__main__':
print Solution().twoSum((2, 7, 11, 15), 9)

C++

1
2
3
4
5
6
7
8
9
10
11
12
13
class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
unordered_map<int, int> lookup;
for (int i = 0; i < nums.size(); ++i) {
if (lookup.count(target - nums[i])) {
return {lookup[target - nums[i]], i};
}
lookup[nums[i]] = i;
}
return {};
}
};