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46 lines
1.4 KiB
C++
46 lines
1.4 KiB
C++
#define _CRT_SECURE_NO_WARNINGS
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#define _SILENCE_CXX17_C_HEADER_DEPRECATION_WARNING
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#include <bits/stdc++.h>
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using namespace std;
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const int N = 1e5 + 50, M = N << 1;
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int adj[N], nxt[M], to[M], ecnt;
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int p[N], dis[N];
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bool bp[N];
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inline void addEdge(int f, int t)
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{
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ecnt++;
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nxt[ecnt] = adj[f];
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adj[f] = ecnt;
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to[ecnt] = t;
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}
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int main()
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{
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int n, k;
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scanf("%d%d", &n, &k);
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for (int i = 1, u, v; i < n; i++)
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scanf("%d%d", &u, &v), addEdge(u, v), addEdge(v, u);
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for (int i = 0; i < k; i++)
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scanf("%d", p + i), bp[p[i]] = true;
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if (p == 0) return puts("0"), 0;
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int h = 0, t = 0;
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static int que[N];
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memset(dis, 0x3f, sizeof(dis));
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for (dis[que[t++] = *p] = 0; h ^ t; h++)
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for (int x, e = adj[x = que[h]]; e; e = nxt[e])
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if (dis[to[e]] > dis[x] + 1)
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dis[que[t++] = to[e]] = dis[x] + 1;
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int mxid = -1, mxval = 0;
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for (int i = 0; i < k; i++)
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if (mxval < dis[p[i]]) mxval = dis[mxid = p[i]];
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h = t = 0;
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memset(dis, 0x3f, sizeof(dis));
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for (dis[que[t++] = mxid] = 0; h ^ t; h++)
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for (int x, e = adj[x = que[h]]; e; e = nxt[e])
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if (dis[to[e]] > dis[x] + 1)
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dis[que[t++] = to[e]] = dis[x] + 1;
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mxid = -1, mxval = 0;
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for (int i = 0; i < k; i++)
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if (mxval < dis[p[i]]) mxval = dis[mxid = p[i]];
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printf("%d", (mxval + 1) >> 1);
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return 0;
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} |