海量数据Top K算法（C实现）

       最近2天受到http://blog.csdn.net/v_JULY_v/archive/2011/05/08/6403777.aspx的影响，从头开始实现了这个算法。收获还是挺大的：（1）实现了Hash链表（2）实现了堆；（3）熟悉了C语言的文件操作；

     海量数据处理的Top K 算法就是在很大的文件中找出重复出现次数最多的前K个字符串；

     如果数据可以一次读入内存，那么可以按照如下思路来解决：

    （1）首先遍历文件，将其加入Hash链表；Hash链表的节点定义为：

typedef struct node{ char *word; int count; struct node *next;}node,*node_ptr;

word指向字符串，count为出现的次数；

   （2）建立一个容量为K的最小堆，然后遍历Hash表中剩下的元素；如果找到了一个元素的count值比这个元素值大，那么交换这个节点和堆顶节点；

     完整全部代码如下：在Eclipse + CDT + mingw 下调试通过

     程序有待完善的地方：

     （1）存在一个位置bug:改变HASHLEN的值，程序崩溃；

      （2）HASH链表的遍历不正确，应该遍历到每一个节点的时候，在判断该节点的next是否为空；

 

     # include <stdio.h># include <string.h># include <malloc.h># include <assert.h># include <stdlib.h>#define HASHLEN 101#define WORDLEN 30#define MAX 100000#define DOMAIN 300#define K 5//Hash链表的节点定义typedef struct node{ char *word; int count; struct node *next;}node,*node_ptr;static node_ptr head[HASHLEN];static node array[K];//Hash函数int hash_function(char *p){ unsigned int value = 0; while (*p != '/0') { value = value * 31 + *p++; if (value > HASHLEN) value = value % HASHLEN; } return value;}//加入节点到HASH链表void append_word(char *str){ int index = hash_function(str); node_ptr p = head[index]; while (p != NULL) { if (strcmp(str, p->word) == 0) { (p->count)++; return; } p = p->next; } // 新建一个结点 node_ptr q = (node_ptr)malloc(sizeof(node)); q->count = 1; q->word = (char *)malloc(sizeof(str) + 1); strcpy(q->word, str);// q->word = str; q->next = head[index]; head[index] = q;}//产生0~DOMAIN - 1范围内的MAX个整数void gen_data(){ FILE *fp = fopen("c://data1.txt", "w"); assert(fp); int i = 0; srand((int)(time(0))); for (i = 0; i < MAX; i++) fprintf(fp,"%d ",rand()%DOMAIN); fclose(fp);}//堆调整:调整为最小堆void heapAdjust(node array[], int beginIndex, int endIndex, int index){int length = endIndex - beginIndex + 1;int largestIndex = index;int leftIndex = 2 * index + 1; //下标从0开始，可以自己做实验int rightIndex = 2 * index + 2;if (leftIndex <= length - 1 && array[leftIndex].count <= array[largestIndex].count ){largestIndex = leftIndex;}if (rightIndex <= length - 1 && array[rightIndex].count <= array[largestIndex].count ){largestIndex = rightIndex;}if (largestIndex != index){node temp = array[largestIndex];array[largestIndex] = array[index];array[index] = temp;heapAdjust (array, beginIndex, endIndex, largestIndex);}}//建堆void heapBuild (node array[], int len ){int i = 0;for (i = len/2 - 1; i >= 0; i --){heapAdjust (array, 0, len - 1, i);}}int main(){gen_data();char str[WORDLEN];//char *str;int i;int cnt1 = 0;for (i = 0; i < HASHLEN; i++) head[i] = NULL;FILE *fp_passage = fopen("c://data1.txt", "r");assert(fp_passage);while (fscanf(fp_passage, "%s", str) != EOF){ cnt1++; append_word(str); }printf("the cnt1 is %d/n", cnt1); fclose(fp_passage); //寻找Top Kfor(i = 0; i < HASHLEN; i++){if(i < K - 1)array[i] = *head[i];elseif(i == K - 1){array[i] = *head[i];heapBuild(array,K);}else{if(array[0].count < head[i]->count){array[0] = *head[i];heapAdjust(array,0,K - 1,0);}}}printf("the top K is as follows/n");for(i = 0; i < K; i++) printf("%s , and its count is %d/n",array[i].word, array[i].count);//printf("the total number of word is %d",cnt);return 0;}

    

   运行结果：

100000个树中重复出现次数最多的前5个数：

the top K is as follows
49 , and its count is 372
4 , and its count is 374
249 , and its count is 373
246 , and its count is 380
227 , and its count is 376