1 // 最小的k个数.cpp : 定义控制台应用程序的入口点。
2 //
3
4 #include "stdafx.h"
5 #include <iostream>
6 #include <set>
7 #include <vector>
8 #include <queue>
9 using namespace std;
10
11 // set中默认是从大到小的顺序，即最先取出的是最小值
12 // 此处为从小到大，最先取出的是最大值
13 typedef multiset<int,greater<int>> inSet;
14 typedef multiset<int,greater<int>>::iterator setIterator;
15
16 // 基于红黑树
17 void GetNumber(vector<int> &data,inSet &leastNumber,int k)
18 {
19 if(k<=0 || data.size()==0)
20 return ;
21 leastNumber.clear();
22 vector<int>::iterator it = data.begin();
23 for(;it!=data.end();++it)
24 {
25 if(leastNumber.size()<k)
26 leastNumber.insert(*it);
27 else{
28 setIterator s = leastNumber.begin();
29
30 if(*it < *s)
31 {
32 leastNumber.erase(s);
33 leastNumber.insert(*it);
34 }
35 }
36 }
37 setIterator s = least.begin();
38 for(;s!=least.end();++s)
39 cout<<*s<<" ";
40 cout<<endl;
41 }
42
43 // 基于优先队列
44 void GetNumber2(vector<int> &data,int k)
45 {
46 if(data.size()==0 || k<1)
47 return ;
48 // top取出的是最小值，即是按从大到小排列的
49 //priority_queue<int,vector<int>,greater<int>> q;
50 // 默认是从小到大排列，即最先取出的是最大值
51 priority_queue<int> q;
52 vector<int>::iterator it = data.begin();
53 for(;it!=data.end();++it)
54 {
55 if(q.size()<k)
56 q.push(*it);
57 else{
58 if(*it < q.top())
59 {
60 q.pop();
61 q.push((*it));
62 }
63 }
64 }
65 while(q.size()>0)
66 {
67 cout<<q.top()<<" ";
68 q.pop();
69 }
70 cout<<endl;
71 }
72
73 int Partition(int *a,int start,int end)
74 {
75 if(start < end)
76 {
77 int i=start,j=end;
78 int x = a[start];
79 while(i<j)
80 {
81 while(i<j && a[j]>x)
82 j--;
83 if(i<j)
84 a[i++] = a[j];
85 while(i<j && a[i]<x)
86 i++;
87 if(i<j)
88 a[j--] = a[i];
89 }
90 a[i] = x;
91 return i;
92 }
93 }
94
95 // 基于分治思想，但会修改数组，时间复杂度为O(N)
96 void GetNumber2(int *a,int len,int k)
97 {
98 if(a==NULL || len<=0 || k<=0)
99 return ;
100 int start = 0,end = len-1;
101 int index = Partition(a,start,end);
102 //取出最小的K个数
103 while(index != k-1)
104 {
105 if(index < k-1)
106 {
107 start = index +1;
108 index = Partition(a,start,end);
109 }else{
110 end = index -1;
111 index = Partition(a,start,end);
112 }
113 }
114 for(int i=0;i<k;++i)
115 cout<<a[i]<<" ";
116 cout<<endl;
117 }
118
119
120 int _tmain(int argc, _TCHAR* argv[])
121 {
122 vector<int> v;
123 v.push_back(1);
124 v.push_back(3);
125 v.push_back(9);
126 v.push_back(2);
127 v.push_back(3);
128 v.push_back(8);
129 v.push_back(6);
130 inSet least;
131 GetNumber1(v,least,5);
132
133 GetNumber2(v,5);
134
135 int a[]={3,1,35,65,7,3,8,2};
136 GetNumber2(a,8,1);
137
138 system("pause");
139 return 0;
140 }
141
