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扑և�数组中最大的K个数

爱吃鱼头 — Wed, 20 Jan 2010 06:05:00 GMT

用的是随机算法�?br />C代码�Q?br />

1 #include <stdio.h>
2 #include <stdlib.h>
3 int new_random(int min, int max)
4 {
5     return (min + (int)(((float)rand()/RAND_MAX)*(max - min)));
6 }
7 void swap(int *a, int *b)
8 {
9     int c = *a;
10     *a = *b;
11     *b = c;
12 }
13
14 int partition(int A[], int p, int r)
15 {
16     int i = p - 1, j;
17     for(j = p; j < r; j++)
18     {
19         if(A[j] <= A[r])
20         {
21             i++;
22             swap(&A[i], &A[j]);
23         }
24     }
25     swap(&A[i + 1], &A[r]);
26     return i + 1;
27 }
28
29 int randomize_partition(int A[], int p, int r)
30 {
31     int i = new_random(p, r);
32     swap(&A[i], &A[r]);
33     return partition(A, p, r);
34 }
35
36 //�W�一�U�算�?/span>
37 int randomized_select(int data[], int p, int r, int k)
38 {
39     if(k > (r - p + 1)) return 0;
40     if(p == r) return data[p];
41     int i = randomize_partition(data, p, r);
42     //int i = partition(data, p, r);
43
44     int count = i - p + 1;
45     if(k <= count)
46         return randomized_select(data, p, i, k);
47     else
48         return randomized_select(data, i + 1, r, k - count);
49 }

Java代码�Q?br />

1 package algorithm;
2
3 import java.util.ArrayList;
4 import java.util.Collections;
5 import java.util.List;
6 import java.util.Random;
7
8 public class FindKth {
9
10     public static Random rand = new Random();
11
12     /**
13      * Find the K-th smallest number in a list using random algorithm
14      *
15      * @return the k-th smallest number
16      */
17     public static int selectKth(int[] arr, int k) {
18         int low = 0;
19         int high = arr.length - 1;
20         int m;
21         k = k - 1;
22         while (low < high) {
23             int r = low + rand.nextInt(high - low + 1);
24             swap(arr, low, r);
25             m = low;
26             for (int i = low + 1; i <= high; i++)
27                 if (arr[i] < arr[low])
28                     swap(arr, ++m, i);
29             swap(arr, low, m);
30             if (m == k)
31                 return arr[k];
32             else if (m < k)
33                 low = m + 1;
34             else
35                 high = m - 1;
36         }
37
38         return arr[k];
39     }
40
41     public static int selectKth(Integer[] arr, int k) {
42         int[] array = new int[arr.length];
43         for (int i = 0; i < arr.length; i++)
44             array[i] = arr[i];
45         return selectKth(array, k);
46     }
47
48     private static void swap(int[] arr, int low, int r) {
49         int tmp = arr[low];
50         arr[low] = arr[r];
51         arr[r] = tmp;
52     }
53
54     /**
55      * @param args
56      */
57     public static void main(String[] args) {
58         List<Integer> list = new ArrayList<Integer>();
59         for (int i = 0; i < 10; i++)
60             list.add(new Integer(i + 1));
61         Integer[] arr = new Integer[list.size()];
62         for (int loop = 0; loop < 1000; loop++) {
63             Collections.shuffle(list);
64             list.toArray(arr);
65             int res = selectKth(arr, 5);
66             if (res != 5)
67                 System.out.println(loop + " " + res);
68         }
69
70     }
71
72 }
73

Python代码�Q?br />

1 #!/usr/bin/env python
2 from random import randint
3
4 # finding the kth smallest number in a list
5 def select(list, k):
6     low = 0
7     up = len(list) - 1
8     k = k - 1
9     while(low < up):
10         rand = randint(low, up)
11         list[low], list[rand] = list[rand], list[low] #swap
12         m = low
13         tmp = list[low]
14         for i in xrange(low + 1, up + 1):
15             if list[i] < tmp:
16                 m += 1
17                 list[m], list[i] = list[i], list[m] # swap
18         list[m], list[low] = list[low], list[m]
19         if m == k:
20             return list[k]
21         elif m < k:
22             low = m + 1
23         elif m > k:
24             up = m - 1
25     return list[k]
26
27
28 x = range(1, 11)
29 from random import shuffle
30 for i in range(100):
31     shuffle(x)
32     print select(x, 5)

爱吃鱼头 2010-01-20 14:05 发表评论

爱吃鱼头 — Sun, 21 Jun 2009 10:09:00 GMT

摘要: 字符串与整数的互相�{�? 以及相应的测试例�?nbsp; 阅读全文

爱吃鱼头 2009-06-21 18:09 发表评论

两个已排序链表的合�ƈ

爱吃鱼头 — Sun, 21 Jun 2009 04:02:00 GMT

1 typedef struct Node{
2     int data;
3     struct Node* next;
4 }Node, *LinkList;
5 void Merge(LinkList la, LinkList lb, LinkList &lc)
6 {
7     // NULL��?/span>
8     if(!la) {lc = pb; return;}
9     if(!lb) {lc = pa; return;}
10     Node* p;
11
12     // ��定最大值在la�? �q�是lb�?/span>
13     if(la.data > lb.data) { lc = p = la; la = la->next; }
14     else { lc = p = lb; lb = lb->next; }
15
16     while(la &&lb)
17     {
18         if(la.data > lb.data)
19         {
20             p->next = la;
21             la = la->next;
22         }else if(la.data < lb.data)
23         {
24             p->next = lb;
25             lb = lb->next;
26         }else{ // la �?nbsp;lb中值相�{�的情况
27             p->next = la;
28             la = la->next;
29             Node* tmp = lb;
30             lb = lb->next;
31             free(tmp);
32         }
33         p = p->next;
34     }
35     // 剩余部分链表的挂�?/span>
36     p->next = (la ? la:lb);
37 }

爱吃鱼头 2009-06-21 12:02 发表评论

爱吃鱼头 — Sat, 20 Jun 2009 17:04:00 GMT

摘要: 有两个相同的栈，一个里面放着自大到小排列的数�Q�栈��的数最��，另一个栈是空�?
不允许利用其它的数据�l�构�Q�只能利用这两个栈，要求把第一个栈里的数字反过来，�?
��到大排列，�l�果�q�放在原来的那个栈里面�?nbsp; 阅读全文

爱吃鱼头 2009-06-21 01:04 发表评论

带通配�W�的字符匚w��

爱吃鱼头 — Mon, 15 Jun 2009 17:02:00 GMT

摘要: 最常见的通配�W�是?�?。其中，?可以代表一个字�W�（不能没有�Q�，*可以代表��L��多个字符�Q�可以�ؓ�I�）�?
首先�?�Q�根�?的功能，?表示��L��字符�Q�也��是说在匚w��q�程中，?永远匚w��成功。本质上�Q?�q�没有修改算法，而仅仅修改了匚w��规则——遇�?则一定匹配�?
然�?与此不同�Q?的作用是匚w��L��多个字符�Q�显然我们不能简单的修改匚w��q�程而满��求。如果我们重新思�?的作用，我们会发�?的另一个作用就是分割P�Ԍ��卛_��果P=P1*P2�Q�那么与其说*代表匚w��L��多个字符�Q�不如说P的匹配条件是在匹配P1子串后再匚w��P2子串�?
因此�Q�可以写出带通配�W�的字符串匹配算�?nbsp; 阅读全文

爱吃鱼头 2009-06-16 01:02 发表评论

�|�络爬虫的一些功能要求整理（转）

爱吃鱼头 — Thu, 04 Jun 2009 13:07:00 GMT

摘要: 摘要�Q�一�Q�一个大定w��的页面文件容器；二、一个高效的HTTP下蝲器；三、一个完善的URL提取器；四、一个便利的�l�构化数据提取器阅读全文

爱吃鱼头 2009-06-04 21:07 发表评论

爱吃鱼头 — Tue, 23 Dec 2008 09:36:00 GMT

Google Base64可以搜到相关原理和许多实现�?br /> 下面是我的实玎ͼ�和SUN公司提供的参考实现�?br />

  1 public class Base64 {
  2     static String base64_alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
  3
  4     /**
  5      * �~�码原理:��?个字节�{换成4个字�? (3 X 8) = 24 = (4 X 6) )
  6      * 先读�?个字�?每读一个字�?左移8�?再右�U�d��?每次6�?�q�样��有4个字节了
  7      *
  8      * @param data
  9      * @return �~�码后的Base64字符�?br /> 10      */
11     public static String Base64Encode(byte[] data) {
12         StringBuilder builder = new StringBuilder();
13         int[] temp = new int[4];
14         int len = data.length - data.length % 3;
15         for (int i = 0; i < len; i += 3) {
16             int goal = 0;
17             for (int j = 0; j < 3; j++) {
18                 goal <<= 8;
19                 goal |= (data[i + j] & 0xff);
20             }
21             for (int k = 0; k < 4; k++) {
22                 temp[k] = goal & 0x3f;
23                 goal >>= 6;
24             }
25             for (int k = 3; k >= 0; k--) {
26                 builder.append(base64_alphabet.charAt(temp[k]));
27             }
28         }
29         int index;
30         switch (data.length % 3) {
31         case 1:
32             index = data[data.length - 1] >> 2;
33             builder.append(base64_alphabet.charAt(index));
34             index = (data[data.length - 1] & 0x03) << 4;
35             builder.append(base64_alphabet.charAt(index));
36             builder.append("==");
37             break;
38         case 2:
39             index = data[data.length - 1 - 1] >> 2;
40             builder.append(base64_alphabet.charAt(index));
41             index = (data[data.length - 1 - 1] & 0x03) << 4
42                     | data[data.length - 1] >> 4;
43             builder.append(base64_alphabet.charAt(index));
44             index = (data[data.length - 1] & 0x0f) << 2;
45             builder.append(base64_alphabet.charAt(index));
46             builder.append('=');
47             break;
48         }
49         return builder.toString();
50     }
51
52     /**
53      * 解码原理:��?个字节�{换成3个字�? 先读�?�?�?用或�q�算),每次左移6�?再右�U?��?每次8�?
54      *
55      * @param data
56      *            需解码的Base64字符丌Ӏ?br /> 57      * @return byte[]�Q�解码出的字节数�l?br /> 58      */
59     public static byte[] Base64Decode(String data) {
60         char[] chArray = data.toCharArray();
61         int len = chArray.length;
62         byte[] result = new byte[len * 3 / 4];
63         for (int i = 0, res_i = 0; i < len; i += 4, res_i += 3) {
64             int goal = 0;
65             int index = 0;
66             for (int k = 0; k < 4; k++) {
67                 index = base64_alphabet.indexOf(chArray[i + k]);
68                 goal <<= 6;
69                 goal |= index;
70             }
71             for (int j = 2; j >= 0; j--) {
72                 result[res_i + j] = (byte) goal;
73                 goal >>= 8;
74             }
75         }
76         // �{�号=的处�?/span>
77         if (chArray[len - 1] != '=')
78             return result;
79         else if (chArray[len - 2] == '=')
80             return Arrays.copyOf(result, result.length - 2);
81         else
82             return Arrays.copyOf(result, result.length - 1);
83
84     }
85 // ��?nbsp;s �q�行 BASE64 �~�码
86     public static String getBASE64(String s) {
87         if (s == null)
88             return null;
89         return (new sun.misc.BASE64Encoder()).encode(s.getBytes());
90     }
91
92     // ��?nbsp;BASE64 �~�码的字�W�串 s �q�行解码
93     public static String getFromBASE64(String s) {
94         if (s == null)
95             return null;
96         BASE64Decoder decoder = new BASE64Decoder();
97         try {
98             byte[] b = decoder.decodeBuffer(s);
99             return new String(b);
100         } catch (Exception e) {
101             return null;
102         }
103     }
104 }

爱吃鱼头 2008-12-23 17:36 发表评论

Java 生成随机序列

爱吃鱼头 — Tue, 23 Dec 2008 09:32:00 GMT

摘要: 从网上�ȝ��的比较好的生成随机序列的��法�Q�）阅读全文

爱吃鱼头 2008-12-23 17:32 发表评论