The use of Priority_queue

Priority_queue essence is a heap.

1. header file is #include<queue>

2. Comparison of elements in Priority_queue

Template declaration with 3 parameters: Priority_queue<type, Container, Functional>, where type is the data type, Container is the container that holds the data, and functional is the element comparison method.

Container must be an array-implemented container, such as Vector,deque, and so on, but not a list. In STL, vectors are used by default.

2.1 Comparison mode by default with OPERATOR<, so if the following 2 parameters default, the priority queue is the Big Top heap (descending), the largest team head element.

The following code returns a descending output:

1#include <iostream>2#include <queue>3 using namespacestd;4 intMain () {5priority_queue<int>Q;6      for(intI=0; i<Ten; ++i) Q.push (i);7      while( !Q.empty ()) {8Cout<<q.top () <<Endl;9 Q.pop ();Ten     } One     return 0; A}

　　

2.2 If you want to use a small top heap, you generally need to take 3 parameters of the template in. The STL defines a functor Greater<>, and the base type can declare a small top heap with this functor .

The following code returns an ascending output:

1#include <iostream>2#include <queue>3 using namespacestd;4 intMain () {5priority_queue<int, vector<int, greater<int> >Q;6      for(intI=0; i<Ten; ++i) Q.push (Ten-i);7      while( !Q.empty ()) {8cout << q.top () <<Endl;9 Q.pop ();Ten     } One     return 0; A}

2.3 For custom types, you must overload operator< or override the functor.

Example of 2.3.1 overloaded operator<: Returns True when the left parameter has a lower priority than the right parameter

1#include <iostream>2#include <queue>3 using namespacestd;4 structnode{5     intx, y;6Node (intA=0,intb=0):7 x (a), Y (b) {}8 };9 BOOL operator< (Node A, Node B) {//returns True, stating that A has a priority lower than BTen     //a node with a large X-value has a low priority (x small node in front of the team) One     //when x is equal, Y has a low priority (Y-small node is in front of the team) A     if(a.x== b.x)returnA.y>b.y; -     returnA.x>b.x; - } the intMain () { -Priority_queue<node>Q; -      for(intI=0; i<Ten; ++i) - Q.push (Node (rand (), rand () )); +      while( !Q.empty ()) { -cout << q.top (). x <<' '<< q.top (). Y <<Endl; + Q.pop (); A     } at     return 0; -}

after the custom type overloads the operator<, the object can be declared with only one template parameter .

But this cannot be declared priority_queue<node,vector<node>,greater<node> like the basic type, because greater<node> is not defined, If you want to define this method, you can overload operator >.

Example: A small top heap is returned. But not how to use, habit is overloaded operator<.

1#include <iostream>2#include <queue>3 using namespacestd;4 structnode{5     intx, y;6Node (intA=0,intb=0 ):7 x (a), Y (b) {}8 };9 BOOL operator> (Node A, Node B) {//return True,a priority is greater than BTen     //x is in the front of the team, and X is at the front of the team. One     if(a.x== b.x)returnA.y>b.y; A     returnA.x>b.x; - } - intMain () { thepriority_queue<node,vector<node>,greater<node> >Q; -      for(intI=0; i<Ten; ++i) - Q.push (Node (rand (), rand () )); -      while( !Q.empty ()) { +cout << q.top (). x <<' '<< q.top (). Y <<Endl; - Q.pop (); +     } A     return 0; at}

2.3.2 Overrides an example of an affine function (the return value sort is the same as 2.3.1, both of which are small top heaps. First by x Ascending, x equal, then y Ascending):

1#include <iostream>2#include <queue>3 using namespacestd;4 structnode{5     intx, y;6Node (intA=0,intb=0 ):7 x (a), Y (b) {}8 };9 structcmp{Ten     BOOL operator() (Node A, Node B) {//The default is the less function One         //when True, the priority of a is lower than the priority of B (A is at the back of B) A         if(a.x== b.x)returnA.y>b.y;  -         returnA.x>b.x;} - }; the intMain () { -Priority_queue<node, Vector<node>, cmp>Q; -      for(intI=0; i<Ten; ++i) - Q.push (Node (rand (), rand () )); +      while( !Q.empty ()) { -cout << q.top (). x <<' '<< q.top (). Y <<Endl; + Q.pop (); A     } at     return 0; -}

Reference: http://www.cnblogs.com/flyoung2008/articles/2136485.html

The use of Priority_queue