暴力

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target)
    {
        int n=nums.size();
        //vector<int> res;
        for (int i = 0; i < nums.size(); i++)
        {
            for (int j = i+1; j < n; j++)
            {
                if (nums[i] + nums[j] == target)
                {
                    // res = vector<int>({j, i});
                    // break
                    return {i,j};
                }
            }
           // if (res.size() > 0) break;
        }
        return {};
    }
};

哈希O(1)

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target)
    {
        vector<int>res;
        unordered_map<int ,int >hash;
        for(int i=0;i<nums.size();i++)
        {
            int a = target-nums[i];
            if(hash.count(a))
            {
                res = vector<int >({hash[a],i});
                break;
            }
            hash[nums[i]] =i;
        }
        return res;

    }
};

leetcode01

原文：https://www.cnblogs.com/xinyi-Conan/p/15179806.html