167. Two Sum II - Input array is sorted

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最新推荐文章于 2020-05-27 04:26:24 发布

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本文介绍了一种在已排序的整数数组中寻找两个数使其和等于特定目标值的有效算法。通过双指针技术，该算法能在O(n)时间内找到符合条件的两个数的下标，展示了算法设计的精妙之处。

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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.

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