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  • Hashing

    Hashing - Hard Version

    Given a hash table of size N, we can define a hash function . 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
    

    分析

    参考Messier
    可以使用拓扑排序来解这道题。基本思路如下:将输入保存在散列表后,遍历每个元素,如果元素刚好在它对应余数的位置上,则入度为0,可直接输出;否则,从余数位置出发,用线性探测法到达该位置,对于经过的所有的非空元素位置,生成一条到该元素位置的边,并将该位置入度加1;拓扑排序时,可以采用优先队列,优先输出数值较小的元素

    代码如下

    #include<iostream>
    #include<queue>
    #include<algorithm> 
    using namespace std;
    vector<int> G[1000]; // 连接表
    int N;
    int indegree[1000]={0}; // 入度
    int a[1000];
    struct mycompare{ // 为优先队列自定义操作
    	bool operator()(int m,int n){
    		return a[m]>a[n];
    	}
    };
    void toposort(){ // 拓扑排序
    	int tag=0;
    	priority_queue<int,vector<int>,mycompare> q;
    	for(int i=0;i<N;i++)
    	if(indegree[i]==0&&a[i]>=0)
    	q.push(i);
    	while(!q.empty()){
    		int t=q.top();
    		if(tag++==0) cout<<a[t];
    		else cout<<" "<<a[t];
    		q.pop();
    		for(int i=0;i<G[t].size();i++){
    			int v=G[t][i];
    			indegree[v]--;
    			if(indegree[v]==0)
    			q.push(v);
    		}
    	} 
    }
    int main(){
    	cin>>N;
    	for(int i=0;i<N;i++)
    	cin>>a[i];
        for(int i=0;i<N;i++){ // 建图
        	if(a[i]%N==i||a[i]<0)
    		continue;
        	else 
    		{
    		    int t=a[i]%N;
        		while(t!=i){
        			G[t].push_back(i);
        			indegree[i]++;
        			t=(t+1)%N;
    			}
    		}
    	}
    	toposort();
    	return 0;
    } 
    
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  • 原文地址:https://www.cnblogs.com/A-Little-Nut/p/8168015.html
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