排序之快速排序

快速排序的在内排中起到比较重要的作用，平均时间复杂度达到O(nlogn)。

升序快速排序

 1 int partition(vector<int> &vi,int start,int end){
 2     int key=vi[start];
 3     while(start<end){
 4         while(start<end&&vi[end]>=key)
 5             end--;
 6         vi[start]=vi[end];
 7         while(start<end&&vi[start]<key)
 8             start++;
 9         vi[end]=vi[start];
10     }
11     vi[start]=key;
12     return start;
13 }
14 void quickCore(vector<int> &vi,int start,int end){
15     if(start<end){
16         int idx =partition(vi,start,end);
17         quickCore(vi,start,idx-1);
18         quickCore(vi,idx+1,end);
19     }
20 }
21 
22 void quickSort(vector<int>&vi){
23     quickCore(vi,0,vi.size()-1);  
24 }

指定排序顺序快速排序

 1 bool cmp(const int &a,const int &b){
 2     return (b-a>=0)?true:false;
 3 }
 4 bool rcmp(const int &a,const int &b){
 5     return (b-a>=0)?false:true;
 6 }
 7 int partition(vector<int> &vi,int start,int end,bool (*cmp)(const int&,const int&)){
 8     int key=vi[start];
 9     while(start<end){
10         while(start<end&&cmp(key,vi[end]))
11             end--;
12         vi[start]=vi[end];
13         while(start<end&&!cmp(key,vi[start]))
14             start++;
15         vi[end]=vi[start];
16     }
17     vi[start]=key;
18     return start;
19 }
20 void quickCore(vector<int> &vi,int start,int end,bool (*cmp)(const int&,const int&)){
21     if(start<end){
22         int idx =partition(vi,start,end,cmp);
23         quickCore(vi,start,idx-1,cmp);
24         quickCore(vi,idx+1,end,cmp);
25     }
26 }
27 
28 void quickSort(vector<int>&vi,bool (*cmp)(const int&,const int&)){
29     quickCore(vi,0,vi.size()-1,cmp);  
30 }

指定任意对象和排序规则的快速排序

 1 struct component{
 2     int a;
 3     int b;
 4 };
 5 bool cmp(const component& obj1,const component& obj2){
 6     if(obj2.a>obj1.a)
 7         return true;
 8     else if(obj2.a<obj1.a)
 9         return false;
10     else if(obj2.b>=obj1.b)
11         return true;
12     return false;
13 }
14 bool rcmp(const component& obj1,const component& obj2){
15     if(obj1.a>obj2.a)
16         return true;
17     else if(obj1.a<obj2.a)
18         return false;
19     else if(obj1.b>=obj2.b)
20         return true;
21     return false;
22 }
23 
24 template<class T>
25 int partition(vector<T> &vi,size_t start,size_t end,bool (*cmp)(const T&,const T&)){
26     T key=vi[start];
27     while(start<end){
28         while(start<end&&cmp(key,vi[end]))
29             end--;
30         vi[start]=vi[end];
31         while(start<end&&!cmp(key,vi[start]))
32             start++;
33         vi[end]=vi[start];
34     }
35     vi[start]=key;
36     return start;
37 }
38 template<class T>
39 void quickCore(vector<T> &vi,size_t start,size_t end,bool (*cmp)(const T&,const T&)){
40     if(start<end){
41         size_t idx =partition(vi,start,end,cmp);
42         quickCore(vi,start,idx-1,cmp);
43         quickCore(vi,idx+1,end,cmp);
44     }
45 }
46 template<class T>
47 void quickSort(vector<T>&vi,bool (*cmp)(const T&,const T&)){
48     quickCore(vi,0,vi.size()-1,cmp);  
49 }

迭代器类型快速排序

 1 struct component{
 2     int a;
 3     int b;
 4 };
 5 bool cmp(const component& obj1,const component& obj2){
 6     if(obj2.a>obj1.a)
 7         return true;
 8     else if(obj2.a<obj1.a)
 9         return false;
10     else if(obj2.b>=obj1.b)
11         return true;
12     return false;
13 }
14 bool rcmp(const component& obj1,const component& obj2){
15     if(obj1.a>obj2.a)
16         return true;
17     else if(obj1.a<obj2.a)
18         return false;
19     else if(obj1.b>=obj2.b)
20         return true;
21     return false;
22 }
23 bool cmp1(const int &a,const int &b){
24     return (b-a>=0)?true:false;
25 }
26 bool rcmp1(const int &a,const int &b){
27     return (b-a>=0)?false:true;
28 }
29 template<class Iterator, class Comparator>
30 Iterator partition(Iterator start,Iterator end,Comparator cmp){
31     typedef typename iterator_traits<Iterator>::value_type value_type;
32     value_type key=*start;
33     while(start!=end-1){
34         while(start!=end-1&&cmp(key,*(end-1)))
35             end--;
36         *start=*(end-1);
37         while(start!=end-1&&!cmp(key,*start))
38             start++;
39         *(end-1)=*start;
40     }
41     *(end-1)=key;
42     return end-1;
43 }
44 template<class Iterator, class Comparator>
45 void quickCore(Iterator start,Iterator end,Comparator cmp){
46     if(start !=end){
47         Iterator idx =::partition(start,end,cmp);
48         quickCore(start,idx,cmp);
49         quickCore(idx+1,end,cmp);
50     }
51 }
52 template<class Iterator, class Comparator>
53 void quickSort(Iterator start,Iterator end,Comparator cmp){
54     quickCore(start,end,cmp);  
55 }
56 template<class Iterator>
57 void quickSort(Iterator start,Iterator end){
58     quickCore(start,end,less<typename iterator_traits<Iterator>::value_type>());  
59 }

测试

 1 #include <iostream>
 2 #include<vector>
 3 #include<algorithm>
 4 #include<set>
 5 using namespace std;
 6 
 7 int main( )
 8 { 
 9     vector<int> vi{1,7,3,1};
10     quickSort(vi.begin(),vi.end());
11     sort(vi.begin(),vi.end(),cmp1);
12     for(int i=0;i<vi.size();i++)
13         cout<<vi[i]<<"  ";
14     cout<<endl;
15     
16     vector<component> obj{
17       {1,4},
18       {3,6},
19       {2,8},
20       {2,7},
21       {1,1}
22     };
23     quickSort(obj.begin(),obj.end(),cmp);
24     for(int i=0;i<obj.size();i++){
25         cout<<obj[i].a<<"  "<<obj[i].b<<endl;
26     }
27     return 0;
28 }