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LeetCode[Hash Table]: Two Sum
Given an array of integers, find two numbers such that they add up to a specific target number.
The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.
You may assume that each input would have exactly one solution.
Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2
Brute force
vector<int> twoSum(vector<int> &numbers, int target) {
vector<int> answer;
for (int i = 0; i < numbers.size() - 1; i++)
for (int j = i + 1; j < numbers.size(); j++)
if (numbers[i] + numbers[j] == target) {
answer.push_back(i + 1);
answer.push_back(j + 1);
return answer;
}
return answer;
}Result: Time Limit Exceeded
Hash table
vector<int> twoSum(vector<int> &numbers, int target) {
vector<int> answer;
map<int, int> numMap;
for (int i = 0; i < numbers.size(); i++)
if (numMap.find(target - numbers[i]) != numMap.end()) {
answer.push_back(numMap[target - numbers[i]] + 1);
answer.push_back(i + 1);
return answer;
}
else numMap[numbers[i]] = i;
return answer;
}LeetCode[Hash Table]: Two Sum
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