add Example 2: capture varialbe in lambda function

Author: keineahnung2345

priority_queue_custom_comparison.cpp

@@ -1,6 +1,8 @@
+  
 #include <iostream>
 #include <queue> //priority_queue
 #include <vector>
+#include <unordered_map>
 
 using namespace std;
 
@@ -12,8 +14,10 @@ class mycomparison{
     }
 };
 
-int main()
-{
+//https://stackoverflow.com/questions/5807735/c-priority-queue-with-lambda-comparator-error
+
+int main(){
+    /***Example 1***/
     priority_queue<int, vector<int>, mycomparison> pq;
     vector<int> v = {1,7,2,9,3,0,4,5,-3,-9,-4,-2};
 
@@ -25,6 +29,45 @@ int main()
         cout << pq.top() << " ";
         pq.pop();
     }
-    //0 1 2 -2 3 -3 4 -4 5 7 -9 9 
+    cout << endl;
+    
+    /***Example 2: capture varialbe in lambda function***/
+    unordered_map<string, int> counter = 
+    	{
+    		{"a", 1},
+    		{"aa",1},
+    		{"aaa",1},
+    		{"b",3},
+    		{"c",2}
+    	};
+    
+    //sort by their count, and then by lexicographical order
+    auto comp = [&counter](const string& lhs, const string& rhs){
+        /*if we want an element to be popped from priority queue earlier,
+        then we need to make it rank lower in the sorted array
+        */
+        // cout << lhs << " " << counter[lhs] << " " << rhs << " " << counter[rhs] << endl;
+        // cout << lhs << " " << rhs << " " << (lhs > rhs) << endl;
+        return (counter[lhs] == counter[rhs]) ? (lhs > rhs) : 
+            (counter[lhs] < counter[rhs]);
+    };
+    
+    priority_queue<string , vector<string>, decltype(comp)> pq2(comp);
+    
+    for(auto it = counter.begin(); it != counter.end(); it++){
+        pq2.push(it->first);
+    }
+    
+    while(!pq2.empty()){
+        cout << pq2.top() << " ";
+        pq2.pop();
+    }
+    cout << endl;
+        
     return 0;
 }
+
+/*
+0 1 2 -2 3 -3 4 -4 5 7 -9 9 
+b c a aa aaa 
+*/