Cod sursa(job #1940384)

Utilizator radu.leonardoThe Doctor radu.leonardo Data 26 martie 2017 16:26:17
Problema Lowest Common Ancestor Scor 0
Compilator cpp Status done
Runda Arhiva educationala Marime 2.64 kb
#include <bits/stdc++.h>
using namespace std;

class Reader
{
public:
    Reader() {}
    Reader(const char *file_name)
    {
        input_file = fopen(file_name, "r");
        cursor = 0;
        fread(buffer, SIZE, 1, input_file);
    }
    inline Reader &operator >>(int &n)
    {
        while(buffer[cursor] < '0' || buffer[cursor] > '9')
        {
            advance();
        }
        n = 0;
        while('0' <= buffer[cursor] && buffer[cursor] <= '9')
        {
            n = n * 10 + buffer[cursor] - '0';
            advance();
        }
        return *this;
    }
private:
    FILE *input_file;
    static const int SIZE = 1 << 17;
    int cursor;
    char buffer[SIZE];
    inline void advance()
    {
        ++ cursor;
        if(cursor == SIZE)
        {
            cursor = 0;
            fread(buffer, SIZE, 1, input_file);
        }
    }
};

class Writer
{
public:
    Writer(const char *name):
        m_stream(name)
    {
        memset(m_buffer, 0, sizeof(m_buffer));
        m_pos = 0;
    }

    Writer& operator<<(int a)
    {
        int many = 0;
        do
        {
            digit_buffer[many++] = a % 10 + '0';
            a /= 10;
        }
        while (a > 0);
        for (int i = many - 1; i >= 0; --i)
            putchar(digit_buffer[i]);
        return *this;
    }

    Writer& operator<<(const char *s)
    {
        for (; *s; ++s)
            putchar(*s);
        return *this;
    }

    ~Writer()
    {
        m_stream.write(m_buffer, m_pos);
    }

private:
    void putchar(char c)
    {
        m_buffer[m_pos++] = c;
        if (m_pos == kBufferSize)
        {
            m_stream.write(m_buffer, m_pos);
            m_pos = 0;
        }
    }

    static const int kBufferSize = 1 << 17;
    ofstream m_stream;
    char m_buffer[kBufferSize];
    char digit_buffer[30];
    int m_pos;
};

int n,m,k=0,h=240;
int V[100001],Dad[100001],Depth[100001];
vector <int> G[100001];
Reader f("lca.in");
Writer g("lca.out");

void read_data()
{
    f>>n>>m;
    for (int i=2;i<=n;i++)
    {
        f>>V[i];
        G[V[i]].push_back(i);
    }
}

void DFS(int node,int parent=0,int level=0)
{
    Depth[node]=level;
    Dad[node]=parent;
    if (level%h==0) parent=node;
    for (auto it:G[node])
        DFS(it,parent,level+1);
}

void compute()
{
    DFS(1);
}

int LCA(int x,int y)
{
    while (Dad[x]!=Dad[y])
        if (Depth[x]>Depth[y]) x=Dad[x];
        else y=Dad[y];

    while (x!=y)
        if (Depth[x]>Depth[y]) x=V[x];
        else y=V[y];

    return x;
}

void solve()
{
    int x,y;
    for(int i=1; i<=m; i++)
    {
        f>>x>>y;
        cout<<LCA(x,y)<<"\n";
    }
}

int main()
{
    read_data();
    compute();
    solve();
}