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Book of Evil

                                        Book of Evil



#include <iostream>
#include <vector>
#include <cstring>
#include <stdio.h>
#define sf(i) scanf("%d", &i)
#define pf(i) printf("%d\n", i)
#define pb push_back
using namespace std;

const int N = 1e5 + 1;
int h[N];
bool mark[N],ans[N];
vector<int> g[N];
int n, m, d, D, R;

void dfs(int s, int p)
{
    h[s] = h[p] + 1;
    ans[s] &= (h[s] <= d);
    if(mark[s] && h[s] > D)
    {
        D = h[s], R = s;
    }

    for(int i = 0; i < g[s].size(); i++)
    {
        int v = g[s][i];
        if(v == p)
            continue;
        dfs(v,s);
    }
}
int main()
{
    sf(n), sf(m), sf(d);
    int a, b;
    D = 0;
    h[0] = -1;

    for(int i = 1; i <= m; i++)
    {
        sf(R);
        mark[R] = true;
    }

    for(int i = 1; i <= n - 1; i++)
    {
        sf(a), sf(b);
        g[a].pb(b);
        g[b].pb(a);
    }

    memset(ans, true, sizeof(ans));

    /* calculate the distance of other vertex from this node and finds the marked node farthest from this marked node */
    dfs(R, 0);
    /* calculate the distance of other vertex from this node and find the farthest marked node from this node */
    dfs(R, 0);
    /* calculate the distance of other vertex from this node */
    dfs(R, 0);

    /*if a node is at most d distance apart from two farthest marked node then that node should be added in the answer */

    int res = 0;
    for(int i = 1; i <= n; i++)
    {
        if(ans[i])
            res++;
    }

    pf(res);
    return 0;
}

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