/* c++ STL is much nore than what i think before in these aspects: * initializer for node element in struct node; * compare function in struct : overload operation * index not iterator used in this function. */class Solution {public:    struct node{    int value;    int order;    node(int v,int index):value(v), order(index){}    };    struct {    bool operator()(node a, node b){    return a.value<=b.value; }    }compare;    vector<int> twoSum(vector<int>& nums, int target) {                vector<int>re;        vector<node>sor;        for(int i=0;i<nums.size();i++)sor.push_back(node(nums[i],i));        sort(sor.begin(),sor.end(),compare);        for(int tmp,i=0,j=sor.size()-1;i<j;)        {            tmp=sor[i].value+sor[j].value;            if(tmp== target)            {                re.push_back(sor[i].order);                re.push_back(sor[j].order);                break;            }            else if(tmp < target)i++;            else j--;        }        return re;    }   };

/* so beautiful and clean* hashmap..........*/public int[] twoSum(int[] nums, int target) {    Map<Integer, Integer> map = new HashMap<>();    for (int i = 0; i < nums.length; i++) {        int complement = target - nums[i];        if (map.containsKey(complement)) {            return new int[] { map.get(complement), i };        }        map.put(nums[i], i);    }    throw new IllegalArgumentException("No two sum solution");}