11-散列4 Hashing

Given a hash table of size N, we can define a hash function H(x)=x%N. Suppose that the linear probing is used to solve collisions, we can easily obtain the status of the hash table with a given sequence of input numbers.

However, now you are asked to solve the reversed problem: reconstruct the input sequence from the given status of the hash table. Whenever there are multiple choices, the smallest number is always taken.

Input Specification:

Each input file contains one test case. For each test case, the first line contains a positive integer N(≤1000), which is the size of the hash table. The next line contains N integers, separated by a space. A negative integer represents an empty cell in the hash table. It is guaranteed that all the non-negative integers are distinct in the table.

Output Specification:

For each test case, print a line that contains the input sequence, with the numbers separated by a space. Notice that there must be no extra space at the end of each line.

Sample Input:

11
33 1 13 12 34 38 27 22 32 -1 21

Sample Output:

1 13 12 21 33 34 38 27 22 32

/*知道散列数组大小，和散列数组值反求输入数组*/
#include<cstdio>
#include<cstdlib>
#include<set>
using namespace std;
const int maxn = 1010;
int G[maxn][maxn];

void BuildGraph(int hash[], int n);
void TopSort(int hash[], int hashMap[], int n, int num);

int main()
{
    int n;
    int num = 0;    //纪录hash表中元素个数 
    int hash[maxn], hashMap[maxn];
    scanf("%d", &n);
    
    for (int i = 0; i < n; i++)
    {
        scanf("%d", &hash[i]);
        hashMap[hash[i]] = i;
        if (hash[i] >= 0)
        {
            num++;
        }
    }
    
    BuildGraph(hash, n);
    TopSort(hash, hashMap, n, num);
    return 0;
}

void BuildGraph(int hash[], int n)
{
    for (int i = 0; i < n; i++)
    {
        if (hash[i] >= 0)
        {
            int tmp = hash[i] % n;    //对应采用线性检查法解决碰撞的元素 
            if (hash[tmp] != hash[i])
            {
                for (int j = tmp; j != i; j = (j+1) % n)    //建立有向拓扑图来 
                {
                    G[j][i] = 1;    //凡是在这个元素之前的位置，都要依赖他们先输入 
                }
            }
        }
    }
}

void TopSort(int hash[], int hashMap[], int n, int num)
{
    int cnt = 0;
    int Indegree[maxn] = {0};
    set<int> s;
    
    for (int v = 0; v < n; v++)
    {
        for(int w = 0; w < n; w++)
        {
            if (G[v][w] != 0)
            {
                Indegree[w]++;
            }
        }
    }
    
    for (int i = 0; i < n; i++)
    {
        if (Indegree[i] == 0 && hash[i] > 0)
        {
            s.insert(hash[i]);
        }
    }
    
    while (!s.empty())
    {
        int now = hashMap[*s.begin()];
        s.erase(s.begin());
        cnt++;
        printf("%d", hash[now]);
        if (cnt != num)
        {
            printf(" ");
        }
        
        for (int v = 0; v < n; v++)
        {
            if (G[now][v] != 0)
            {
                if (--Indegree[v] == 0)
                {
                    s.insert(hash[v]);
                }
            }
        }
    }
}