C++實現 LeetCode-1.Two Sum

方法一：Brute Force

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> arr;
        if(nums.size() <= 1)
            return arr;
        for(int i = 0; i<nums.size(); ++i){
            for(int j = i+1;j<nums.size();++j){
                int rest = target - nums[i];
                if(nums[j] == rest){
                    arr.push_back(i);
                    arr.push_back(j);
                    return arr;
                }
            }
        }
    }
};

方法二：map（ Map是STL的一個關聯容器，它提供一對一的數據處理能力）

class Solution{
    public:
    vector<int> twoSum(vector<int>& nums,int target){
        vector<int> ret;
        if(nums.size() <= 1)
            return ret;
        map<int,int> mymap;
        for(int i=0;i<nums.size();++i)
            mymap[nums[i]]=i;
        for(int i=0;i<nums.size();++i){
            int rest=target-nums[i];
            if(mymap.find(rest)!=mymap.end()){
                int index = mymap[rest];
                if(index==i)
                    continue;
                if(index<i){
                    ret.push_back(index);
                    ret.push_back(i);
                    return ret;
                }else{
                    ret.push_back(i);
                    ret.push_back(index);
                    return ret;
                }
            }
        }
    }
};