LeetCode-Solution/C++/sort-characters-by-frequency.cpp at master · paperfactory/LeetCode-Solution · GitHub

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// Time: O(n)

// Space: O(n)

class Solution {

public:

string frequencySort(string s) {

unordered_map<char, int> freq;

for (const auto& c : s) {

++freq[c];

}

vector<string> counts(s.size() + 1);

for (const auto& kvp : freq) {

counts[kvp.second].push_back(kvp.first);

}

string result;

for (int count = counts.size() - 1; count >= 0; --count) {

for (const auto& c : counts[count]) {

result += string(count, c);

}

return result;

}

};