167. Two Sum II - Input array is sorted

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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

因為sort過，可以使用two pointer的方式來縮小range

   public int[] twoSum(int[] numbers, int target) {
        int lo = 0, hi = numbers.length - 1;
        while(lo < hi){
            
            if(target == numbers[lo] + numbers[hi]){
                return new int[]{lo+1, hi+1};
            }
            else if( target > numbers[lo] + numbers[hi]){
                lo++;
            }
            else
                hi--;
            
        }
        return new int[]{0,0};
    }