Introduction Link to heading
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 Link to heading
Simple solution:
func twoSum(numbers []int, target int) []int {
for i, n := range numbers {
if j, ok := binarySearch(numbers[i+1:], target-n); ok {
return []int {i+1, i+1+j+1}
}
}
return nil
}
func binarySearch(arr []int, val int) (int, bool) {
low, hi := 0, len(arr)-1
for low <= hi {
mid := low + (hi-low) / 2
v := arr[mid]
if v == val {
return mid, true
} else if v > val {
hi = mid - 1
} else if v < val {
low = mid + 1
}
}
return 0, false
}
Explanation Link to heading
Binary search solution.