51 lines
1.8 KiB
C++
51 lines
1.8 KiB
C++
class cmp{
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public:
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// this is how we overload the function call operator, and this has to a public method.
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bool operator() (std::pair<string,int> p1, std::pair<string,int> p2){
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if(p1.second==p2.second){
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// lexicographical order
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return (p1.first < p2.first);
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}else{
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// sort this way would make sure the top of the heap is the string with the lowest frequency.
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return (p1.second > p2.second);
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}
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}
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};
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class Solution {
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public:
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vector<string> topKFrequent(vector<string>& words, int k) {
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int size = words.size();
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// map words to frequency
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unordered_map<string, int> u_map1;
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vector<string> v1;
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// establish the map
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for(int i=0;i<size;i++){
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u_map1[words[i]]++;
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}
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// define a priority queue (MAX heap) with a custom comparison function
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priority_queue<pair<string, int>,vector<pair<string,int>>,cmp> pq;
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// traverse the map so as to establish the priority queue.
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unordered_map<string, int>::iterator itr;
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itr = u_map1.begin();
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while(itr != u_map1.end()){
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// push each pair into u_map1.
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pq.push(*itr);
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if(pq.size()>k){
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// evict the string with the lowest frequency?
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pq.pop();
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}
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itr++;
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}
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// after the above for loop, pq will have a size of k, and contains the strings with the highest frequency.
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// now just move these strings into v1.
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for(int i=0;i<k;i++){
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// we have to use top() here, beause pop() won't return anything.
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v1.push_back((pq.top()).first);
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pq.pop();
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}
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std:reverse(v1.begin(),v1.end());
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return v1;
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}
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};
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