167. Two Sum II

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. 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 and you may not use the same element twice.

Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2

数组常sort

public int[] twoSum(int[] numbers, int target) {
        //返回一个数组,包含头尾指针
      
        int[]ans=new int[2];
         //健壮性判断
         
        if(numbers==null||numbers.length<2)return ans;
        int left=0;
        int right=numbers.length-1;
        while(left<right){
            int sum=numbers[left]+numbers[right];
            if(sum==target){
                ans[0]=++left;
                ans[1]=++right;
                break;
                }else if(sum>target){
                    right--;
                }else left++;
        }
        return ans;
    }