Priority Queue of Vectors in C++ STL with Examples

• Difficulty Level : Medium
• Last Updated : 17 Mar, 2020

Priority Queue in STL Priority queues are a type of container adapters, specifically designed such that the first element of the queue is the greatest of all elements in the queue and elements are in non increasing order(hence we can see that each element of the queue has a priority{fixed order})

Vector in STL Vector is same as dynamic arrays with the ability to resize itself automatically when an element is inserted or deleted, with their storage being handled automatically by the container. Vector elements are placed in contiguous storage so that they can be accessed and traversed using iterators.

Priority Queue of Vectors in STL: Priority Queue of Vectors can be very efficient in designing complex data structures.

Syntax:

```priority_queue<vector<datatype>> pq;
```

For example: Consider a simple problem where we have to print the maximum vector that is in the queue.

 `// C++ program to demonstrate ` `// use of priority queue for vectors ` ` `  `#include ` `using` `namespace` `std; ` ` `  `priority_queue > pq; ` ` `  `// Prints maximum vector ` `void` `Print_Maximum_Vector(vector<``int``> Vec) ` `{ ` `    ``for` `(``int` `i = 0; i < Vec.size(); i++) { ` `        ``cout << Vec[i] << ``" "``; ` `    ``} ` `    ``cout << endl; ` `    ``return``; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``// Initializing some vectors ` `    ``vector<``int``> data_1{ 10, 20, 30, 40 }; ` `    ``vector<``int``> data_2{ 10, 20, 35, 40 }; ` `    ``vector<``int``> data_3{ 30, 25, 10, 50 }; ` `    ``vector<``int``> data_4{ 20, 10, 30, 40 }; ` `    ``vector<``int``> data_5{ 5, 10, 30, 40 }; ` ` `  `    ``// Inserting vectors into priority queue ` `    ``pq.push(data_1); ` `    ``pq.push(data_2); ` ` `  `    ``// printing the maximum vector till now ` `    ``Print_Maximum_Vector(pq.top()); ` ` `  `    ``// Inserting vectors into priority queue ` `    ``pq.push(data_3); ` ` `  `    ``// printing the maximum vector till now ` `    ``Print_Maximum_Vector(pq.top()); ` ` `  `    ``// Inserting vectors into priority queue ` `    ``pq.push(data_4); ` `    ``pq.push(data_5); ` ` `  `    ``// printing the maximum vector till now ` `    ``Print_Maximum_Vector(pq.top()); ` ` `  `    ``return` `0; ` `} `

Output:

```10 20 35 40
30 25 10 50
30 25 10 50
```

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