167. Two Sum II - Input array is sorted(easy)

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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方法。通过双指针技巧，算法在O(n)时间内找到满足条件的两个数的下标，适用于LeetCode题目“两数之和II - 输入有序数组”。

Easy

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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.

C++:

/*
 * @Author: SourDumplings
 * @Link: https://github.com/SourDumplings/
 * @Email: changzheng300@foxmail.com
 * @Description: https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/
 * @Date: 2019-04-17 22:37:25
 */

class Solution
{
public:
    vector<int> twoSum(vector<int> &numbers, int target)
    {
        int n = numbers.size();
        vector<int> ret(2);
        for (int i = 0; i < n - 1; i++)
        {
            int thisTarget = target - numbers[i];
            for (int j = i + 1; j < n; j++)
            {
                if (numbers[j] == thisTarget)
                {
                    ret[0] = i + 1;
                    ret[1] = j + 1;
                    return ret;
                }
                else if (numbers[j] > thisTarget)
                {
                    break;
                }
            }
        }
        return ret;
    }
};