Cod sursa(job #3266153)

Utilizator TraianQTraianQ TraianQ Data 6 ianuarie 2025 09:24:06
Problema Lowest Common Ancestor Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.03 kb
#include <fstream>
#include <vector>
using namespace std;
vector <int> V[100005];
int depth[100005],dp[100005][21];
void dfs(int x)
{
    for(auto a:V[x])
    {
        depth[a]=depth[x]+1;
        dfs(a);
    }
}
int lca(int x,int y)
{
    if(depth[x]<depth[y])
        swap(x,y);
    for(int i=19;i>=0;i--)
        if(depth[x]-(1<<i)>=depth[y])
            x=dp[x][i];
    if(x==y)
        return x;
    for(int i=19;i>=0;i--)
        if(dp[x][i]!=dp[y][i])
        {
            x=dp[x][i];
            y=dp[y][i];
        }
    return dp[x][0];
}
int main()
{
    ifstream fin("lca.in");
    ofstream fout("lca.out");
    int n,m,a;
    fin>>n>>m;
    for(int i=2;i<=n;i++)
    {
        fin>>a;
        dp[i][0]=a;
        V[a].push_back(i);
    }
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=19;j++)
            dp[i][j]=dp[ dp[i][j-1] ][j-1];
    }
    dfs(1);
    int x,y;
    for(int i=1;i<=m;i++)
    {
        fin>>x>>y;
        fout<<lca(x,y)<<'\n';
    }
    return 0;
}