Source:https://leetcode.com/problems/two-sum/
Time: 2020/11/15
Description:
Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.
You can return the answer in any order.
Example 1:
Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Output: Because nums[0] + nums[1] == 9, we return [0, 1].
Example 2:
Input: nums = [3,2,4], target = 6
Output: [1,2]
Example 3:
Input: nums = [3,3], target = 6
Output: [0,1]
Constraints:
2 <= nums.length <= 105
-109 <= nums[i] <= 109
-109 <= target <= 109
Only one valid answer exists.
Solution
Bruce force would cause TLE
Approach1:
Two-pass Hash Table
class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
map<int, int> mp;
for(int i = 0; i < nums.size(); i++)
mp[nums[i]] = i;
for(int i = 0; i < nums.size(); i++)
{
map<int, int>::iterator iter = mp.find(target - nums[i]);
if(iter != mp.end() && iter->second != i)
return {
i, iter->second};
}
throw invalid_argument("the input has no solution");
}
};
Approach2:
One-pass Hash Table
class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
map<int, int> mp;
for(int i = 0; i < nums.size(); i++)
{
map<int, int>::iterator iter = mp.find(target - nums[i]);
if(iter != mp.end())
return {
iter->second, i};
mp[nums[i]] = i;
}
throw invalid_argument("the input has no solution");
}
};