Two Sum II - Input array is sorted

Desicription

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:

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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

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class Solution {
public:
vector<int> twoSum(vector<int>& numbers, int target) {
for(int left = 0, right = numbers.size()-1; left < right; ) {
if(numbers[left] + numbers[right] > target)
right--;
else if(numbers[left] + numbers[right] < target)
left++;
else if(numbers[left] + numbers[right] == target)
return vector<int>{left+1, right+1};
}
}
};