CODEWITHSUNDEEP
c++unordered-map
George An
George An

Reputation: 11

Am I using find wrong?

I'm trying to find string tp inside an unordered_map but it's giving me problems.

unordered_map < string, int > pastPoints;
int t = 0;
void doStuff(int x, int y) {
    pair < int, int > tp_ = {x, y};
    string tp = int_string(tp_);
    if (find(pastPoints.begin(), pastPoints.end(), tp) != pastPoints.end()) {
        ans = max(ans, t - pastPoints[tp]);
    }
    pastPoints[tp] = t;
}

It's giving me this error:

error: no match for ‘operator==’ (operand types are ‘std::pair<conststd::basic_string<char>, int>’ and ‘const std::basic_string<char>’)
{ return *__it == _M_value; }

Am I using unordered_map::find wrong? I'm finding the key which is a string.

Upvotes: 1

Views: 65

Answers (1)

HolyBlackCat
HolyBlackCat

Reputation: 96941

Yes, you're using it wrong.

Don't use std::find with maps and sets. It will check the elements one by one, while maps/sets have a faster way to search for elements.

Do this: pastPoints.find(tp).

Also using pastPoints[tp] after a successful find is wasteful, since it searches the map again. Instead, dereference the iterator returned by find.

Example:

if (auto it = pastPoints.find(tp); it != pastPoints.end())
    ans = max(ans, t - *it);

Upvotes: 1

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