快速排序

时间：2016-01-26 22:00:53 阅读：331 评论：0 收藏：0 [点我收藏+]

填坑之作。

那天因为在考试，就没有听到学长讲。后来听得似懂非懂的。

在《啊哈算法》里面看了一下看懂了。原理很简单，看看代码就懂了。

顺便玩了一下，比较冒泡排序、快速排序、sort排序（qsort因为要指针知识，本人完全不懂）的排序速度快慢

先随机生成10^7个数字……嗯，50多MB。调用rand()之前要srand(time(NULL));初始化。

 1 #include <cstdio>
 2 #include <iostream>
 3 #include <cmath>
 4 #include <cstring>
 5 #include <queue>
 6 #include <vector>
 7 #include <algorithm>
 8 #include <ctime>
 9 #include <cstdlib>
10 
11 #define rep(i,a,n) for(int i = a;i < n;i++)
12 #define per(i,a,n) for(int i = n-1;i >=a;i--)
13 #define pb push_back
14 #define VI vector<int>
15 #define QI queue<int>
16 
17 typedef long long ll;
18 
19 using namespace std;
20 
21 const int MOD = 1e7+8;
22 const int N  = 1e7+8;
23 
24 int main(){
25     freopen("data.in","w",stdout);
26     srand(time(NULL));
27     printf("%d ",N);
28 
29     rep(i,0,N){
30         printf("%d ",rand() % MOD);
31     }puts("");
32     return 0;
33 }

View Code

然后冒泡排序：

 1 #include <cstdio>
 2 #include <iostream>
 3 #include <cmath>
 4 #include <cstring>
 5 #include <queue>
 6 #include <vector>
 7 
 8 #define rep(i,a,n) for(int i = a;i < n;i++)
 9 #define per(i,a,n) for(int i = n-1;i >=a;i--)
10 #define pb push_back
11 #define VI vector<int>
12 #define QI queue<int>
13 
14 typedef long long ll;
15 
16 using namespace std;
17 
18 const int N = 100000000;
19 int n;
20 int a[N] = {};
21 
22 void bubblesort(){
23     rep(i,0,n-1){
24         rep(j,0,n-1){
25             if(a[j] > a[j+1]){
26                 int t = a[j];a[j] = a[j+1];a[j+1] = t;
27             }
28         }
29     }
30 }
31 
32 int main(){
33     freopen("data.in","r",stdin);
34     scanf("%d",&n);
35     rep(i,0,n){
36         scanf("%d",&a[i]);
37     }
38     bubblesort();
39     freopen("data_bubble.out","w",stdout);
40     rep(i,0,n){
41         printf("%d ",a[i]);
42     }puts("");
43     return 0;
44 }

View Code

接着快速排序：

 1 #include <cstdio>
 2 #include <iostream>
 3 #include <cmath>
 4 #include <cstring>
 5 #include <queue>
 6 #include <vector>
 7 
 8 #define rep(i,a,n) for(int i = a;i < n;i++)
 9 #define per(i,a,n) for(int i = n-1;i >=a;i--)
10 #define pb push_back
11 #define VI vector<int>
12 #define QI queue<int>
13 
14 typedef long long ll;
15 
16 using namespace std;
17 
18 const int N = 100000000;
19 int a[N] = {};
20 int n;
21 
22 void quicksort(int l,int r){
23     int flag = a[l];
24     int i = l;
25     int j = r;
26     if(l > r ) return;
27 
28     while(i != j){
29         while(a[j] >= flag && i < j) j--;
30 
31         while(a[i] <= flag && i < j) i++;
32 
33         if(i < j){
34             int t = a[i];a[i] = a[j];a[j] = t;
35         }
36     }
37     a[l] = a[i];
38     a[i] = flag;
39 
40     quicksort(l,i-1);
41     quicksort(i+1,r);
42 }
43 
44 int main(){
45     freopen("data.in","r",stdin);
46     scanf("%d",&n);
47     rep(i,0,n){
48         scanf("%d",&a[i]);
49     }
50     quicksort(0,n-1);
51     freopen("data_quicksort.out","w",stdout);
52     rep(i,0,n){
53         printf("%d ",a[i]);
54     }puts("");
55     return 0;
56 }

View Code

最后，当当~sort排序（据同学说里面内置了三种函数：快速排序，冒泡排序，桶排序？然后哪个排的快选哪个）：

 1 #include <cstdio>
 2 #include <iostream>
 3 #include <cmath>
 4 #include <cstring>
 5 #include <queue>
 6 #include <vector>
 7 #include <algorithm>
 8 
 9 #define rep(i,a,n) for(int i = a;i < n;i++)
10 #define per(i,a,n) for(int i = n-1;i >=a;i--)
11 #define pb push_back
12 #define VI vector<int>
13 #define QI queue<int>
14 
15 typedef long long ll;
16 
17 using namespace std;
18 
19 const int N = 10000000;
20 int n;
21 int a[N] = {};
22 
23 bool cmp(int a,int b){
24     return a < b;
25 }
26 
27 
28 int main(){
29     freopen("data.in","r",stdin);
30     scanf("%d",&n);
31     rep(i,0,n){
32         scanf("%d",&a[i]);
33     }
34     sort(a,a+n,cmp);
35     freopen("data_sort.out","w",stdout);
36     rep(i,0,n){
37         printf("%d ",a[i]);
38     }puts("");
39     return 0;
40 }