1078 Hashing (25point(s)) - C語言 PAT 甲級

1078 Hashing (25point(s))

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 H(key)=key%TSize 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 (≤10⁴) and N (≤MSize) 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 -

題目大意：

輸入散列表長度 Msize，若不是素數，需要重新賦值爲第一個比它大的素數，和 N 個數據依次插入散列表，散列函數爲 H(key)=key%TSize，解決衝突用正向的平方探測法

輸出每個數據插入的位置，無法插入用 -

設計思路：

1. 輸入的 Msize 若不是素數，需要重新賦值爲第一個比它大的素數
2. 平方探測法 index = (key + i * i) % size

編譯器：C (gcc)

#include <stdio.h>

int isprime(int n)
{
        if (n == 1)
                return 0;
        int i;
        for (i = 2; i * i <= n; i++)
                if (n % i == 0)
                        return 0;
        return 1;
}

int hash[10007], size;

void insert(int key)
{
        int index, i;
        for (i = 0; i < size; i++) {
                index = (key + i * i) % size;
                if (hash[index] == 0) {
                        hash[index] = 1;
                        printf("%d", index);
                        return ;
                }
        }
        putchar('-');
}

int main(void)
{
        int n;
        int i, key;

        scanf("%d%d", &size, &n);
        while (!isprime(size))
                size++;
        for (i = 0; i < n; i++) {
                scanf("%d", &key);
                if (i != 0)
                        printf(" ");
                insert(key);
        }
        return 0;
}