Cod sursa(job #682534)

Utilizator claudiumihailClaudiu Mihail claudiumihail Data 19 februarie 2012 04:15:22
Problema Stramosi Scor 80
Compilator cpp Status done
Runda Arhiva de probleme Marime 4.38 kb
#include <fstream>
#include <iostream>
#include <vector>
#include <queue>
#include <cstdlib>

#define MAXN 250001

using namespace std;

typedef unsigned int uint32;
typedef vector<vector<int> >Graph;

Graph graph;

int LookupTable[] =
{
    31, 30, 29, 28, 27, 26, 25, 24,
    23, 22, 21, 20, 19, 18, 17, 16,
    15, 14, 13, 12, 11, 10, 9, 8,
    7, 6, 5, 4, 3, 2, 1, 0
};

struct Identity
{
    Identity() :
        level(0),
        id(0)
    {}
    
    Identity(const unsigned char l, const int iid) :
        level(l),
        id(iid)
    {}

    unsigned char level;
    int id;
};

inline int GetMSB(const int mask)
{
    unsigned long res=0;

#ifdef _MSC_VER
    _BitScanReverse(&res, mask);
#else
    res = LookupTable[__builtin_clz(mask)];
#endif
    
    return res;
}

char matAncestorsSize[MAXN];
int matAncestors[19][MAXN];

int Query(int id, int degree)
{
    if (!degree)
        return id;

    while (degree && matAncestorsSize[id])
    {
        const int idMask = (1<<matAncestorsSize[id])-1;
        int msbIndex = GetMSB(degree & idMask);
        //cout << "MSB = " << msbIndex << endl;
        
        degree -= (1<<msbIndex);
        id = matAncestors[msbIndex][id];
        
        //cout << id << endl;
        //getchar();
    }
    
    if (degree)
    {
        return 0;
    }
    
    //cout << "Acestor is " << id << endl;
    
    return id;
}

int curLevel=0;
int parentID;
int level;
void ConstructAncestorMap(const int currentID)
{
    level = 1;
    parentID = matAncestors[0][currentID];
    
    while ((1<<(level)) <= curLevel)
    {
        parentID = matAncestors[level-1][parentID];
        matAncestors[level][currentID] = parentID;
        matAncestorsSize[currentID]++;
        level++;
    }
    
    curLevel++;
    for (uint32 i=0; i<graph[currentID].size(); ++i)
    {
        matAncestors[0][graph[currentID][i]] = currentID;
        matAncestorsSize[graph[currentID][i]] = 1;
        
        ConstructAncestorMap(graph[currentID][i]);
    }
    curLevel--;
}

int main()
{
    int n, m;
    //AncestorMatrix matAncestors;
    vector<int> vRoots;
    fstream fin("stramosi.in", fstream::in);
    fstream fout("stramosi.out", fstream::out);

    fin >> n >> m;
    //cout << n << " " << m << "\n";

    graph.resize(n+1);
    
    for (int i=1; i<=n; ++i)
    {
        int x;
        fin >> x;
        
        if (!x)
        {
            vRoots.push_back(i);
        }
        else
        {
            graph[x].push_back(i);
        }
    }
    
    for (uint32 i=0; i<vRoots.size(); ++i)
    {
       // cout << vRoots[i] << " ";
       
       ConstructAncestorMap(vRoots[i]);
    }
    //cout << "\n";
    
    /*for (uint32 i=1; i<=n; ++i)
    {
        cout << i << "-> ";
        for (uint32 j=0; j<graph[i].size(); ++j)
        {
            cout << graph[i][j] << " ";
        }
        cout << "\n";
    }*/
    
    /*int curQ = 0;
    int curLevel = 0;
    queue<int> Q[2];
    for (uint32 i=0; i<vRoots.size(); ++i)
    {
        Q[curQ].push(vRoots[i]);
    }
    
    while (!Q[curQ].empty() || !Q[!curQ].empty())
    {
        while (!Q[curQ].empty())
        {
            int currentID = Q[curQ].front();
            Q[curQ].pop();

            int level = 1;
            int parentID = matAncestors[0][currentID];
            
            while ((1<<(level)) <= curLevel)
            {
                parentID = matAncestors[level-1][parentID];
                matAncestors[level][currentID] = parentID;
                matAncestorsSize[currentID]++;
                level++;
            }
            
            for (uint32 i=0; i<graph[currentID].size(); ++i)
            {
                matAncestors[0][graph[currentID][i]] = currentID;
                matAncestorsSize[graph[currentID][i]] = 1;
                Q[!curQ].push(graph[currentID][i]);
            }
        }
        
        curLevel++;
        curQ = !curQ;
    }*/
    
    /*cout << "Size = " << matAncestors[13].size() << endl;
    for (uint32 i=0; i<matAncestors[13].size(); ++i)
    {
        cout << matAncestors[13][i] << endl;
    }*/
    
    for (int i=0; i<m; ++i)
    {
        int p,q;
        
        fin >> q >> p;
        fout << Query(q, p) << "\n";
    }

    fin.close();
    fout.close();
    return 0;
}