hdu4821 string 字符串 哈希处理

  1. 常用哈希函数,seed=131,初始化阶数组,方便等阶后比较,初始化字符串,比较时只需要看差值。
  2. 逆向初始化字符串,使当前元素在差值中。
  3. 利用集合的大小是否符合要求判断是否有重复。

题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=4821

 #include<cstdio>
 #include<iostream>
 #include<sstream>
 #include<cstdlib>
 #include<cmath>
 #include<cctype>
 #include<string>
 #include<cstring>
 #include<algorithm>
 #include<stack>
 #include<queue>
 #include<set>
 #include<map>
 #include<ctime>
 #include<vector>
 #include<fstream>
 #include<list>

 #define ms(s) memset(s,0,sizeof(s))
 #define pri(mark,i) printf("%s: %d\n",mark,i)
 #define prs(mark,s) printf("%s: %s\n",mark,s)
 #define prd(mark,d) printf("%s: %lf\n",mark,d)
 typedef long long LL;
 typedef unsigned long long ULL;

 using namespace std;

 map<ULL,int>maps;

 #define L 100000
 int seed = 131;
 ULL base[L+5];
 ULL hv[L+5];
 char str[L+5];
 int len;

 void initBase()
 {
     base[0] = 1;
     for(int i = 1; i <= L; ++i)
         base[i] = base[i-1]*seed;
 }
 void initHv()
 {
     len = strlen(str);
     hv[len] = 0;
     for(int i = len-1; i >= 0; --i)
         hv[i] = hv[i+1]*seed + str[i];
 }
 ULL getHash(int x, int l)
 {
    return hv[x] - hv[x+l]*base[l];
 }


 int main()
 {
     int m,l;
     int countt;
     initBase();

     int i;
     int j,k;
     ULL t;
     pair<ULL,int>p;
     map<ULL,int>::iterator it;

     while(scanf("%d%d",&m,&l) != EOF)
     {
         scanf("%s",str);
         countt = 0;

         initHv();

         i = 0;
         while(i < l && i < len - m*l)
         {
             maps.clear();
             j = i;
             k = j + m*l;

             for(int c = 1; c <= m; ++c)
             {
                 t = getHash(j,l);
 // pri("t",t);
                 it = maps.find(t);
                 if(it == maps.end())
                 {
                     p.first = t;
                     p.second = 1;
                     maps.insert(p);
                 }
                 else
                     (it->second)++;
                 j+=l;
             }
             if(maps.size() == m)
             {
                 countt++;
 // pri("countt",countt);pri("i",i);pri("j",i);
             }


             j = i + l;
             k += l;
             while(k <= len)
             {
                 t = getHash(j-l,l);
                 maps[t]--;
                 if(maps[t] == 0)
                     maps.erase(t);

                 t = getHash(k-l,l);
                 it = maps.find(t);
                 if(it == maps.end())
                 {
                     p.first = t;
                     p.second = 1;
                     maps.insert(p);
                 }
                 else
                     (it->second)++;
                 if(maps.size() == m)
                 {
                     countt++;
 // pri("countt",countt);pri("i",i);pri("j",j);
                 }

                 j += l;
                 k += l;
             }
             ++i;
         }
         printf("%d\n",countt);
     }





     return 0;
 }
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