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two-sum-ii-input-array-is-sorted

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Two Sum II - Input array is sorted – LeetCode 167

Problem

Description

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.

Example

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

Answer

Original

Code

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

思路

简单使用两个循环分别处理两个字符串的共有段和私有段，从尾向头传播。时间复杂度$O(n)$，空间复杂度$O(1)$。
耗时$6$ ms，排名$81.21\%$

Better

思路

暂时还没看到更好的思路