LeetCode每日一题（ 两数之和）

1.O(n^2)
暴力做法

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> ans;
        for(int i=0; i<nums.size(); i++){
            for(int j=0; j<nums.size(); j++){
                if(i==j) continue;
                if(nums[i]+nums[j]==target){
                    ans.push_back(i);
                    ans.push_back(j);
                    break;
                }
            }
            if(ans.size()!=0) break;
        }
        return ans;
    }
};

2.O(n*log(n))
利用map进行查找

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> ans;
        map<int,int> mp;
        for(int i=0; i<nums.size(); i++){
            if(i==0){
                mp.insert({nums[i],i});
                continue;
            }
            if(mp.find(target-nums[i])!=mp.end()){
                ans.push_back(mp[target-nums[i]]);
                ans.push_back(i);
                break;
            }
            else mp.insert({nums[i],i});
        }
        return ans;
    }
};