two sum
描述
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
vector<int > twoSum( vector<int> &num, int target) {
unordered_map<int , int> mapping ;
vector<int > result;
for (int i = 0; i < num.size (); i++) {
mapping[num[i]] = i;
}
for (int i = 0; i < num.size (); i++) {
const int gap = target - num [i ];if (mapping .find (gap ) != mapping. end() && mapping [gap ] > i) {//因为i 之前的都已经遍历过了result .push_back (i +1);result .push_back (mapping [gap ]+1);break;}
}
return result ;
}
