PAT 甲级 1078 Hashing (25 分)（简单，平方二次探测）

1078 Hashing (25 分)

 

The task of this problem is simple: insert a sequence of distinct positive integers into a hash table, and output the positions of the input numbers. 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 two positive numbers: MSize (≤) and N (≤) which are the user-defined table size and the number of input numbers, respectively. Then N distinct positive integers are given in the next line. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print the corresponding positions (index starts from 0) of the input numbers in one line. All the numbers in a line are separated by a space, and there must be no extra space at the end of the line. In case it is impossible to insert the number, print "-" instead.

Sample Input:

4 4
10 6 4 15

Sample Output:

0 1 4 -

题意：

输入msize和N,如果msize不是素数的话就把msize变为比当前值大的最小素数，采用平方探测方法，求插入哈希表后元素的序号

题解：

平方探测方法

二次探测——
       

                        
    
　　其中，h是哈希寻址函数，key是要存储的值，M是哈希表的大小，一般使用素数可以达到一个较高的效率。

AC代码 ：

#include<bits/stdc++.h>
using namespace std;
int m,n;
int a[20005];
bool prime(int x){
    if(x<=1) return false;
    for(int i=2;i*i<=x;i++){
        if(x%i==0) return false;
    }
    return true;
}
int main(){
    cin>>m>>n;
    for(int i=0;i<20000;i++) a[i]=-1;
    while(!prime(m)) m++;
    int x;
    for(int i=1;i<=n;i++){
        cin>>x;
        int f=0;
        for(int j=0;j<m;j++){
            int y=(x+j*j)%m;//平方探测
            if(a[y]==-1 || a[y]==x){
                cout<<y;
                a[y]=x;
                f=1;
                break;
            }
        }
        if(!f) cout<<"-";
        if(i!=n) cout<<" ";
    }
    return 0;
}