pat 1145

1145 Hashing - Average Search Time (25分)

 

The task of this problem is simple: insert a sequence of distinct positive integers into a hash table first. Then try to find another sequence of integer keys from the table and output the average search time (the number of comparisons made to find whether or not the key is in the table). The hash function is defined to be ( where TSize is the maximum size of the hash table. Quadratic probing (with positive increments only) is used to solve the collisions.
Note that the table size is better to be prime. If the maximum size given by the user is not prime, you must re-define the table size to be the smallest prime number which is larger than the size given by the user.

Input Specification:

Each input file contains one test case. For each case, the first line contains 3 positive numbers: MSize, N, and M, which are the user-defined table size, the number of input numbers, and the number of keys to be found, respectively. All the three numbers are no more than 1. Then N distinct positive integers are given in the next line, followed by M positive integer keys in the next line. All the numbers in a line are separated by a space and are no more than 1.

Output Specification:

For each test case, in case it is impossible to insert some number, print in a line X cannot be inserted. where X is the input number. Finally print in a line the average search time for all the M keys, accurate up to 1 decimal place.

Sample Input:

4 5 4
10 6 4 15 11
11 4 15 2

Sample Output:

15 cannot be inserted.
2.8

题意：模拟平方探测法（只正向探测），求给定带查找关键字的平均查找长度。

注意点：对于不存在的关键字，查找结束的地方是未被插入元素的地方或者平方探测的参数i已经超过了tablesize。

代码如下：

#include<cstdio>
int table[10005]={0};
int getPrime(int n){
    while(true){
        int mark=0;
        for(int i=2;i<n;i++){
            if(n%i==0){
                mark=1;
                break;
            }
        }
        if(mark==0)
            return n;
        n++;
    }

}
int main(){
    int size,num,m;
    scanf("%d%d%d",&size,&num,&m);
    size=getPrime(size);
    int temp;
    for(int i=0;i<num;i++){
        scanf("%d",&temp);
        int j=0;
        for(;j<size;j++){
            if(table[(temp+j*j)%size]==0){
                table[(temp+j*j)%size]=temp;
                break;
            }
        }    
        if(j==size)
            printf("%d cannot be inserted.
",temp);
    }
    int ans=0;
    for(int i=0;i<m;i++){
        scanf("%d",&temp);
        int j=0;
    
        for(;j<=size;j++){
            ans++;
            if(table[(temp+j*j)%size]==0||table[(temp+j*j)%size]==temp)
                break; 
        }
    }
    printf("%0.1lf
",ans/(m*1.0));
    return 0;
}