LeetCode Two Sum II - Input array is sorted

Posted 2020-06-29 Dylan_Java_NYC

原题链接在这里：https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/

题目：

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.

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

题解：

说指针从两头向中间递进. 类似Two Sum.

Time Complexity: O(n). Space: O(1).

AC Java:

 1 public class Solution {
 2     public int[] twoSum(int[] numbers, int target) {
 3         int [] res = new int[]{-1,-1};
 4         if(numbers == null || numbers.length < 2){
 5             return res;
 6         }
 7         int l = 0;
 8         int r = numbers.length-1;
 9         while(l<r){
10             if(numbers[l] + numbers[r] < target){
11                 l++;
12             }else if(numbers[l] + numbers[r] > target){
13                 r--;
14             }else{
15                 res[0] = l+1;
16                 res[1] = r+1;
17                 break;
18             }
19         }
20         return res;
21     }
22 }