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

时间复杂度O(n*n),超时

class Solution {
public:

vector<int> twoSum(vector<int> &numbers, int target) {
vector<int> result;
sort(numbers.begin(),numbers.end());
for(int i = 0; i < numbers.size() - 1; i++)
{
for(int j = i + 1; j <= numbers.size() - 1; j++)
{
if(numbers[i] + numbers[j] == target)
{
//下标从1开始
result.push_back(i + 1);
result.push_back(j + 1);
break;
}
}
}
return result;
}
};采用map函数

class Solution {
public:

vector<int> twoSum(vector<int> &numbers, int target) {
vector<int> result;
map<int,int>myMap;
map<int,int>::iterator it;

for(int i = 0; i < numbers.size(); i++)
{
it = myMap.find(numbers[i]);
if(it != myMap.end())//查找到
{
result.push_back((*it).second);
result.push_back(i + 1);
break;
}
//利用target-numbers[i]作为key，i+1作为value
else
{
int tmp = target - numbers[i];
myMap[tmp] = i + 1;
}
}
return result;
}
};