: HashMap to store key → value mapping

valueToKeys: HashMap to store value → ordered set of keys mapping

Update Operation:

If key exists, remove it from old value's set in valueToKeys
Add/update key in keyToValue
Add key to new value's set in valueToKeys
Clean up empty sets to save memory

Get Operation:

Simple lookup in keyToValue

Max Key Operation:

Look up the ordered set for the given value
Return the maximum element (last element in sorted order)

Edge Cases:

Handle non-existent keys and values
Clean up empty sets after removals

Code

[{"language":"C++","code":"class Solution {\nprivate:\n    unordered_map<int, int> keyToValue;\n    unordered_map<int, set<int>> valueToKeys;\n    \npublic:\n    void update(int key, int val) {\n        // Remove from old value's set if key exists\n        if (keyToValue.find(key) != keyToValue.end()) {\n            int oldVal = keyToValue[key];\n            valueToKeys[oldVal].erase(key);\n            if (valueToKeys[oldVal].empty()) {\n                valueToKeys.erase(oldVal);\n            }\n        }\n        \n        // Update key-value mapping\n        keyToValue[key] = val;\n        \n        // Add to new value's set\n        valueToKeys[val].insert(key);\n    }\n    \n    optional<int> get(int key) {\n        auto it = keyToValue.find(key);\n        if (it != keyToValue.end()) {\n            return it->second;\n        }\n        return nullopt;\n    }\n    \n    optional<int> maxKey(int val) {\n        auto it = valueToKeys.find(val);\n        if (it != valueToKeys.end() && !it->second.empty()) {\n            return *it->second.rbegin();\n        }\n        return nullopt;\n    }\n    \n    void remove(int key) {\n        auto it = keyToValue.find(key);\n        if (it != keyToValue.end()) {\n            int val = it->second;\n            keyToValue.erase(it);\n            \n            valueToKeys[val].erase(key);\n            if (valueToKeys[val].empty()) {\n                valueToKeys.erase(val);\n            }\n        }\n    }\n};","lang":"cpp","html":"<pre class=\"shiki shiki-themes github-light github-dark\" style=\"background-color:#fff;--shiki-dark-bg:#24292e;color:#24292e;--shiki-dark:#e1e4e8\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">class</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\"> Solution</span><span style=\"color:#24292

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