hdu1880 hash算法学习

来源：互联网发布：如何求最大公约数算法编辑：程序博客网时间：2024/05/01 08:47

本题用的是bkdr算法，传说中java内置的hash就是这个实现的

unsigned int BKDRHash(char*str) {     unsigned int seed=131 ;// 31 131 1313 13131 131313 etc..      unsigned int hash=0 ;          while(*str)     {         hash=hash*seed+(*str++);     }          return(hash % M); }

这题我木有A，题解也没咋看懂，虽然网上都说该题很水，，附上保存防丢失。。

//bkdr hash模板#include <cstdio>#include <cstring>#include <cstdlib>#include <algorithm>using namespace std;const int MAX=210000;const int mod=100007;struct Node{Node* ne;char st[81];}hash[MAX],*h[mod],*cur;unsigned int BKDHash(char* s){unsigned int seed=131;unsigned int ret=0;while(*s){ret=ret*seed+*s++;}return (ret&0x7FFFFFFF)%mod;}int getId(char* s){int code=BKDHash(s);Node* ptr=h[code];while(ptr){if(strcmp(ptr->st,s)==0){return ptr-hash;}else{ptr=ptr->ne;}}strcpy(cur->st,s);cur->ne=h[code];h[code]=cur++;return cur-hash-1;}int find(char* s){int code=BKDHash(s);Node* ptr=h[code];while(ptr){if(strcmp(ptr->st,s)==0){return ptr-hash;}else{ptr=ptr->ne;}}return -1;}int main(){char s[100],*p;int id,n;cur=hash;memset(h,0,sizeof(h));while(scanf("%s",s),s[0]!='@'){getId(s);getchar();gets(s);getId(s);}scanf("%d",&n);gets(s);while(n--){gets(s);id=find(s);if(id==-1){puts("what?");}else{p=hash[id^1].st;if(p[0]!='['){puts(p);}else{p++;while(*p!=']'){putchar(*p++);}puts("");}}}return 0;}

对hash算法有兴趣的话，这里很全，，http://blog.csdn.net/hqd_acm/article/details/5901955

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