example3_custom_hash.cpp

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#include <iostream>
#include <unordered_map>
#include <string>

struct CaseInsensitiveHash {
    size_t operator()(const std::string& key) const {
        size_t hash = 0;
        for (char c : key) {
            hash = hash * 31 + std::tolower(c);
        }
        return hash;
    }
};

struct CaseInsensitiveEqual {
    bool operator()(const std::string& left, const std::string& right) const {
        return std::equal(left.begin(), left.end(), right.begin(), right.end(),
                          [](char a, char b) { return std::tolower(a) == std::tolower(b); });
    }
};

int main() {
    std::unordered_multimap<std::string, int, CaseInsensitiveHash, CaseInsensitiveEqual> umm;
    
    umm.insert({"Apple", 1});
    umm.insert({"apple", 2});
    umm.insert({"APPLE", 3});

    for (const auto& pair : umm) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }

    return 0;
}