LeetCode-E-Two Sum

題意

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

解法

排序 ＋ 雙指針

實現

bool mycompare(pair<int,int> a, pair<int,int> b){
    return a.first < b.first;
}
class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> result;
        if(nums.size() == 0) return result;
        vector<pair<int,int>> ivector;
        for(int i = 0; i < nums.size(); ++i){
            ivector.push_back(make_pair(nums[i],i));
        }
        std::sort(ivector.begin(),ivector.end(),mycompare);
        int start = 0; 
        int end = ivector.size() - 1;
        while(start < end){
            int sum = ivector[start].first + ivector[end].first;
            if(sum == target){
                result.push_back(ivector[start].second);
                result.push_back(ivector[end].second);
                return result;
            }else if(sum < target){
                ++start;
            }else --end;
        }
        return result;
    }
};