Today when I was doing leetcode 406, I met with a problem about operator overload. Specifically, I want to move the iterator to a certain position. I want to use operator = to achieve that. But when I finish the overload operator code, compiler shows an error:

overloaded 'operator =' must be a binary operator (has 3 parameters)
    std::list<vector<int>>::iterator operator  = (list<vector<int>>& it, int a) {

I don't know the meaning of that. Here is the code:

struct myclass {
    bool operator() (vector<int>& a, vector<int>& b) {
        if(a[0] == b[0]) return a[1] < b[1]; // if the height is same, the one with smaller k is prior!
        return (a[0] > b[0]);
    }
} compare;

class Solution {
public:  
    std::list<vector<int>>::iterator operator  = (list<vector<int>>& it, int a) {
        while(a-- > 0) {
            it  ;
        }
    }
    vector<vector<int>> reconstructQueue(vector<vector<int>>& people) {
        sort(people.begin(), people.end(), compare);
        list<vector<int>> que;
        for(int i = 0; i < people.size(); i  ) {
            int pos = people[i][1];
            std::list<vector<int>>::iterator it = que.begin();
            it  = pos;
            que.insert(it, people[i]);
        }
        return vector<vector<int>>(que.begin(), que.end());
    }
};

CodePudding user response：

You were probably trying to "fix" the compiler error in the line

it  = pos;

operator = has to have a specific syntax according to the standard. If implemented as non-static member function, it will always have a hidden (except for C 23 deduced this) first parameter pointing to the class instantiation (*this of type Solution in your case).

The issue is caused by the container type you chose: std::list has a (legacy) bidirectional iterator. That means you can only increase (e.g. it) or decrease (e.g. --it) it. If you'd would have used e.g. std::vector, there would be a (legacy) random access iterator, and operator = would already be defined.

It's often not a good idea to implement arithmetic operators for standard library types: they were not implemented in the first place for a reason.

Like mch said in the comments, the standard library has a function to increase the iterator a specific number of times: std::advance. I.e., the line can be replaced with

std::advance(it,pos);

CodePudding user response：

When you do operator overloading as a non-static member function of a class, it is assumed that the first operand is the object through with the function is being called(non-static member functions are always called through an object), in other words, *this.

So to avoid that, in your case(because you don't have access to the definition of the class list::iterator), define the operator = in a static context(outside the Solution class).

Another way would be to create a subclass to inherit the std::iterator and then make some adjustments to the code. There you can directly overload the operator =. But that would just be overkill.

Also why are you passing a list as the first argument? Shouldn't it be an iterator? I am assuming that is a typo.