Leetcode-two sum

Previously, it was done through hash, O (n ). In order to get familiar with the universal solution, we use double pointers. The time complexity is O (nlogn) (that is, the complexity of sort ).

I am not familiar with sort usage and about custom sort rules.

The sample code in C ++ reference is as follows:

 1 // sort algorithm example 2 #include <iostream>     // std::cout 3 #include <algorithm>    // std::sort 4 #include <vector>       // std::vector 5  6 bool myfunction (int i,int j) { return (i<j); } 7  8 struct myclass { 9   bool operator() (int i,int j) { return (i<j);}10 } myobject;11 12 int main () {13   int myints[] = {32,71,12,45,26,80,53,33};14   std::vector<int> myvector (myints, myints+8);               // 32 71 12 45 26 80 53 3315 16   // using default comparison (operator <):17   std::sort (myvector.begin(), myvector.begin()+4);           //(12 32 45 71)26 80 53 3318 19   // using function as comp20   std::sort (myvector.begin()+4, myvector.end(), myfunction); // 12 32 45 71(26 33 53 80)21 22   // using object as comp23   std::sort (myvector.begin(), myvector.end(), myobject);     //(12 26 32 33 45 53 71 80)24 25   // print out content:26   std::cout << "myvector contains:";27   for (std::vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)28     std::cout << ‘ ‘ << *it;29   std::cout << ‘\n‘;30 31   return 0;32 }

We can see that in addition to writing the Compare function, we can also rewrite the circular brackets () to write function objects.

At the beginning, a Compare function was written.

Bool compare (const node & LHS, const node & RHs) {return LHS. Val <RHS. Val;
}
It seems that only the internal part of class solution can be submitted for leetcode. When the Compare function is placed inside solution, an error occurs, and the Compare function is placed outside solution. Why ???
Then, the function object is written through the heavy-load parentheses and passed smoothly.

 1 class Solution {//two sum O(nlogn) 2 public: 3     struct Node{ 4         int val; 5         int index; 6         Node(int v, int idx) :val(v), index(idx){} 7     }; 8     struct myclass { 9         bool operator() (Node n1, Node n2) { return (n1.val<n2.val); }10     } myobject;11 12     vector<int> twoSum(vector<int> &numbers, int target) {13         vector<Node> a;14         for (int i = 0; i < numbers.size(); i++)15         {16             a.push_back(Node(numbers[i], i + 1));17         }18         sort(a.begin(), a.end(),myobject );19         int i = 0, j = numbers.size() - 1;20         vector<int> res;21         while (i < j)22         {23             int sum = a[i].val + a[j].val;24             if (sum == target)25             {26                 int minIndex = min(a[i].index,a[j].index);27                 int maxIndex = max(a[i].index, a[j].index);28                 res.push_back(minIndex);29                 res.push_back(maxIndex);30                 break;31             }32             else if (sum < target)33             {34                 i++;35             }36             else37             {38                 j--;39             }40         }41         return res;42     }43 };

 

Leetcode-two sum