[隊內測試Day10.22T4][洛谷P2680]運輸計劃
阿新 • • 發佈:2019-02-08
吐槽下考場上的魔改題面……
看出來是運輸計劃後,記得以前聽說過是二分,於是開始摸魚……
不會樹鏈剖分,考場上卡掉一個點
儘管實現步驟很麻煩,但思路清晰的話,具體打起來還是比較容易的一道題
能摸出來大概是人品比較好……
#include<iostream>
#include<cstdio>
#include<algorithm>
#define LL long long
using namespace std;
const LL MAXN = 300000 + 50;
struct edge{
LL f,t,v;
}l[MAXN << 1 ];
struct zt{
LL f,t;
LL v;
LL lca;
}e[MAXN];
LL head[MAXN],next[MAXN << 1],tot;
void init(LL n){
for(LL i = 1;i <= n;i ++){
head[i] = -1;
}
}
void build(LL f,LL t,LL v){
l[++ tot] = (edge){f,t,v};
next[tot] = head[f];
head[f] = tot;
}
LL n,m,a,b,c;
LL deep[MAXN],fa[MAXN][26 ];
LL ru[MAXN];
LL rank[MAXN];
void dfs(LL p,LL f){
for(LL i = 1;i <= 25;i ++){
fa[f][i] = fa[fa[f][i - 1]][i - 1];
}
for(LL i = head[f];i != -1;i = next[i]){
LL t = l[i].t;
if(t == p)continue;
ru[t] ++;
deep[t] = deep[f] + 1;
fa[t][0] = f;
rank[t] = rank[f] + l[i].v;
dfs(f,t);
}
}
LL LCA(LL a,LL b){
if (deep[a] < deep[b])swap(a,b);
LL t = deep[a] - deep[b];
for(LL i = 0;i <= 25;i ++){
if(t & (1 << i)){
a = fa[a][i];
}
}
if(a == b)return a;
for(LL i = 25;i >= 0;i --){
if(fa[a][i] != fa[b][i]){
a = fa[a][i];
b = fa[b][i];
}
}
return fa[a][0];
}
LL topo[MAXN];
LL L = 1,R = 1;
void toposort(){
topo[R ++] = 1;
while(L != R){
LL u = topo[L];
for(LL i = head[u];i != -1;i = next[i]){
LL t = l[i].t;
ru[t] --;
if(!ru[t])topo[R ++] = t;
}
L ++;
}
}
LL mid;
LL cf[MAXN];
bool check(LL x){
LL cnt = 0;
LL maxx = 0;
for(LL i = 0;i <= n;i ++){
cf[i] = 0;
}
for(LL i = 1;i <= m;i ++){
if(e[i].v > x){
cf[e[i].f] ++;
cf[e[i].t] ++;
cf[e[i].lca] --;
cf[fa[e[i].lca][0]] --;
cnt ++;
maxx = max(maxx,e[i].v);
}
}
for(LL j = n;j >= 1;j --){
LL u = topo[j];
for(LL i = head[u];i != -1;i = next[i]){
LL t = l[i].t;
if(deep[t] < deep[u])continue;
cf[u] += cf[t];
}
}
for(LL u = 1;u <= n;u ++){
if(cf[u] < cnt)continue;
for(LL i = head[u];i != -1;i = next[i]){
if(deep[l[i].t] < deep[u])continue;
if(cf[l[i].t] >= cnt){
if(maxx - l[i].v <= x)return true;
}
}
}
return false;
}
void solve(){
R ++;
L --;
while(R - L > 1){
mid = L + R >> 1;
if(check(mid))R = mid;
else L = mid;
}
}
int main(){
freopen("Random.in","r",stdin);
freopen("Random.out","w",stdout);
scanf("%lld%lld",&n,&m);
init(n);
for(LL i = 1;i <= n - 1;i ++){
scanf("%lld%lld%lld",&a,&b,&c);
build(a,b,c);
build(b,a,c);
}
dfs(1,1);
toposort();
L = R = 0;
for(LL i = 1;i <= m;i ++){
scanf("%lld%lld",&e[i].f,&e[i].t);
LL lca = LCA(e[i].f,e[i].t);
e[i].v = rank[e[i].f] + rank[e[i].t] - 2*rank[lca];
e[i].lca = lca;
R = max(R,e[i].v);
}
solve();
printf("%lld",R);
fclose(stdin);
fclose(stdout);
return 0;
}