bzoj 2599 [IOI2011]Race 未调完_点分治
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// luogu-judger-enable-o2 // luogu-judger-enable-o2 #include <bits/stdc++.h> #define setIO(s) freopen(s".in","r",stdin) #define maxn 1000000 #define inf 0x7f7f7f using namespace std; int hd[maxn],to[maxn],nex[maxn],val[maxn],f[maxn],vis[maxn],siz[maxn],dep[maxn],ans,cur=0; int cnt,n,k,root,sn,d[2]; void addedge(int u,int v,int c) { nex[++cnt] = hd[u],hd[u] = cnt,to[cnt] = v,val[cnt] = c; } struct Point{ int dis,tot; Point(int dis = 0,int tot = 0):dis(dis),tot(tot){} bool operator<(Point b)const{ return b.dis != dis ? b.dis>dis : b.tot > tot; } }point[2][maxn]; void getdis(int u,int fa,int tot) { point[cur][++d[cur]]=Point(dep[u],tot); for(int i = hd[u]; i ; i = nex[i]) { if(vis[to[i]] || to[i] == fa) continue; dep[to[i]] = dep[u] + val[i],getdis(to[i],u,tot + 1); } } void GetRoot(int u,int ff) { siz[u] = 1,f[u] = 0; for(int i = hd[u]; i ; i = nex[i]) { if(vis[to[i]] || to[i] == ff) continue; GetRoot(to[i],u); siz[u] += siz[to[i]]; f[u] = max(f[u], siz[to[i]]); } f[u] = max(f[u], sn - siz[u]); if(f[u] < f[root]) root = u; } void DFS(int u) { vis[u] = 1, dep[u] = 0, cur = 0, d[cur] = 0,d[cur^1] = 1,point[cur^1][1] = Point(0,0); for(int i = hd[u]; i ; i = nex[i]) { if(vis[to[i]]) continue; dep[to[i]] = val[i]; d[cur] = 0; root = 0,sn = siz[to[i]],GetRoot(to[i],u), DFS(root); getdis(to[i],0,1); sort(point[cur]+1,point[cur]+1+d[cur]); int m = 1; for(int j = 2;j <= d[cur]; ++j) if(point[cur][j].dis!=point[cur][j-1].dis) point[cur][++m]=point[cur][j]; d[cur] = m; int p1 = 1,p2 = d[cur^1]; while(p1 <= d[cur] && p2 >=1) { if(point[cur][p1].dis + point[cur^1][p2].dis == k) ans = min(ans,point[cur][p1].tot + point[cur^1][p2].tot), ++p1,--p2; if(point[cur][p1].dis + point[cur^1][p2].dis < k) ++p1; if(point[cur][p1].dis + point[cur^1][p2].dis > k) --p2; } for(int j = 1;j <= d[cur]; ++j) point[cur^1][++d[cur^1]] = point[cur][j]; sort(point[cur^1]+1,point[cur^1]+1+d[cur^1]); m = 1; for(int j=2;j<=d[cur^1];++j) if(point[cur^1][j].dis!=point[cur^1][j-1].dis)point[cur^1][++m]=point[cur^1][j]; d[cur^1]=m, d[cur]=0; } } int main() { setIO("input"); scanf("%d%d",&n,&k); for(int i = 1,a,b,c;i < n; ++i) scanf("%d%d%d",&a,&b,&c),addedge(a+1,b+1,c),addedge(b+1,a+1,c); ans = inf, vis[0] = 1,f[0] = inf,sn = n,root = 0, GetRoot(1,0),DFS(root); printf("%d\n",ans==inf?-1:ans); return 0; }
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