[每日 LeetCode] 167. Two Sum II - Input array is sorted

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.

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.

思路：本题是 Two Sum 基础版的升级，考虑使用从两边同时扫描的办法，如果两个数的和小于 target，左边右移一位，如果两个数的和大于 target，右边左移一位，直到左右两边相遇。

C++ 代码

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

运行时间：8ms

运行内存：9.6M