Cod sursa(job #2973388)

Utilizator PatruMihaiPatru Mihai PatruMihai Data 31 ianuarie 2023 20:56:33
Problema Lowest Common Ancestor Scor 90
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 3.14 kb
#include <bits/stdc++.h>

using namespace std;

class InParser
{
private:
    FILE *fin;
    char *buff;
    int sp;

    char read_ch()
    {
        ++sp;
        if (sp == 4096)
        {
            sp = 0;
            fread(buff, 1, 4096, fin);
        }
        return buff[sp];
    }

public:
    InParser(const char *nume)
    {
        fin = fopen(nume, "r");
        buff = new char[4096]();
        sp = 4095;
    }

    InParser &operator>>(int &n)
    {
        char c;
        while (!isdigit(c = read_ch()) && c != '-');
        int sgn = 1;
        if (c == '-')
        {
            n = 0;
            sgn = -1;
        }
        else
        {
            n = c - '0';
        }
        while (isdigit(c = read_ch()))
        {
            n = 10 * n + c - '0';
        }
        n *= sgn;
        return *this;
    }

    InParser &operator>>(long long &n)
    {
        char c;
        n = 0;
        while (!isdigit(c = read_ch()) && c != '-');
        long long sgn = 1;
        if (c == '-')
        {
            n = 0;
            sgn = -1;
        }
        else
        {
            n = c - '0';
        }
        while (isdigit(c = read_ch()))
        {
            n = 10 * n + c - '0';
        }
        n *= sgn;
        return *this;
    }
};
class OutParser {
private:
    FILE *fout;
    char *buff;
    int sp;

    void write_ch(char ch) {
        if (sp == 50000) {
            fwrite(buff, 1, 50000, fout);
            sp = 0;
            buff[sp++] = ch;
        } else {
            buff[sp++] = ch;
        }
    }


public:
    OutParser(const char* name) {
        fout = fopen(name, "w");
        buff = new char[50000]();
        sp = 0;
    }
    ~OutParser() {
        fwrite(buff, 1, sp, fout);
        fclose(fout);
    }

    OutParser& operator << (int vu32) {
        if (vu32 <= 9) {
            write_ch(vu32 + '0');
        } else {
            (*this) << (vu32 / 10);
            write_ch(vu32 % 10 + '0');
        }
        return *this;
    }

    OutParser& operator << (long long vu64) {
        if (vu64 <= 9) {
            write_ch(vu64 + '0');
        } else {
            (*this) << (vu64 / 10);
            write_ch(vu64 % 10 + '0');
        }
        return *this;
    }

    OutParser& operator << (char ch) {
        write_ch(ch);
        return *this;
    }
    OutParser& operator << (const char *ch) {
        while (*ch) {
            write_ch(*ch);
            ++ch;
        }
        return *this;
    }
};

InParser fin("lca.in");
OutParser fout("lca.out");

const int NMAX = 1e5 + 7;
vector<vector<int>> v(NMAX);
int dad[NMAX], lvl[NMAX];

void dfs(int nod, int lv)
{
    lvl[nod] = lv;
    for (int i: v[nod])
    {
        dfs(i, lv + 1);
    }
}

int lca(int x, int y)
{
    if (lvl[x] < lvl[y])
        swap(x, y);

    while (lvl[x] > lvl[y])
        x = dad[x];

    while (x != y)
        y = dad[y], x = dad[x];

    return x;
}

int main()
{
    int n, q;
    fin >> n >> q;

    for (int nod = 2; nod <= n; nod++)
    {
        fin >> dad[nod];
        v[dad[nod]].push_back(nod);
    }

    dfs(1, 1);

    while (q--)
    {
        int x, y;
        fin >> x >> y;
        fout << lca(x, y) << "\n";
    }

    return 0;
}