hdu 4607 Park Visit

求树的直径

#include <stdio.h>   #include <string.h>const int MAXN = 100010;struct node{int to, next;}data[MAXN*2];int head[MAXN], n, m, sz;void add(int u, int v){data[sz].to = v;data[sz].next = head[u];head[u] = sz++;data[sz].to = u;data[sz].next = head[v];head[v] = sz++;}int fnum[MAXN], snum[MAXN], cnt[MAXN];void dfs(int u, int pre){int v, i;fnum[u] = snum[u] = 0;for (i = head[u]; ~i; i=data[i].next){if ( (v=data[i].to) == pre) continue;dfs(v, u);if (fnum[v]+1 > fnum[u]){snum[u] = fnum[u];fnum[u] = fnum[v]+1;}else if (fnum[v]+1 > snum[u]){snum[u] = fnum[v]+1;}}i = head[u];if (u != 1)if (i == -1 || data[i].next == -1)/// leaf node{fnum[u]=snum[u] = 0;cnt[u] = 0;return;}int c1=0, c2=0;for (i = head[u]; ~i; i=data[i].next){if ( (v=data[i].to) == pre) continue;if (fnum[u] == fnum[v]+1) c1++;else if (snum[u] == fnum[v]+1) c2++;}if (c1 >= 2){cnt[u] = fnum[u]*2;}else if (c1 >= 1 && c2 >= 1){cnt[u] = fnum[u]+snum[u];}elsecnt[u] = fnum[u];}int main(){#ifndef ONLINE_JUDGE    freopen("in.txt", "r", stdin);#endif // ONLINE_JUDGEint t;scanf("%d", &t);while (t--){scanf("%d%d", &n, &m);sz = 0;memset(head, -1, sizeof head);for (int i = 1; i< n; i++){int u, v;scanf("%d%d", &u, &v);add(u, v);}dfs(1, -1);int mx = 0;for (int i = 1; i<= n; ++i){if (cnt[i] > mx) mx=cnt[i];}++mx;for (int i = 0; i< m; ++i){scanf("%d", &sz);if (sz <= mx)printf("%d\n", sz-1);elseprintf("%d\n", mx-1+(sz-mx)*2);}}    return 0;}