# 167. Two Sum II - Input array is sorted
Given an array of integers that is already sorted in ascending order, 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.
Note:
- Your returned answers (both index1 and index2) are not zero-based.
- You may assume that each input would have exactly one solution and you may not use the same element twice. Example:
Input: numbers = [2,7,11,15], target = 9
Output: [1,2]
Explanation: The sum of 2 and 7 is 9. Therefore index1 = 1, index2 = 2.
# Solution
Approach 1: Two pointers.
# Code (Python)
Approach 1:
# Code (C++)
Approach 1:
class Solution {
public:
vector<int> twoSum(vector<int>& numbers, int target) {
vector<int> res;
int head = 0;
int tail = numbers.size() - 1;
while (head < tail)
{
int sum = numbers[head] + numbers[tail];
if (sum == target)
{
res.push_back(head+1);
res.push_back(tail+1);
break;
}
else if (sum < target)
head++;
else
tail--;
}
return res;
}
};