迷啊……调了一下午……
为什么我把splay时的update方式改成“splay最后再upt(u)一下”就不RE了……
求大神解答……？
题目链接
题解
将边按照a排序，然后从小到大枚举，加入图中。
在图中用lct维护一棵两点之间b最大值尽量小的生成树。
当加入一条边(u, v)时：
如果(u, v)不连通，则直接加入这条边
如果(u, v)连通且它们间路径上的b最大值大于当前边的b，则删除路径上b最大的边，然后加入当前边。
否则这条边没用，啥也不干。
#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <ctime>
#include <cstdlib>
using namespace std;
typedef unsigned long long ll;
#define enter putchar('\n')
#define space putchar(' ')
template <class T>
void read(T &x){
char c;
bool op = 0;
while(c = getchar(), c > '9' || c < '0')
if(c == '-') op = 1;
x = c - '0';
while(c = getchar(), c >= '0' && c <= '9')
x = x * 10 + c - '0';
if(op) x = -x;
}
template <class T>
void write(T x){
if(x < 0) putchar('-'), x = -x;
if(x >= 10) write(x / 10);
putchar('0' + x % 10);
}
const int N = 150005, M = 100005, INF = 0x3f3f3f3f;
int n, m, pcnt, ans = INF;
int fa[N], ls[N], rs[N], val[N], num[N]; //val和num存的都是边的编号
bool rev[N];
struct Edge {
int u, v, a, b, p;
bool operator < (const Edge &obj) const{
return a == obj.a ? b < obj.b : a < obj.a;
}
} e[M];
#define which(u) (ls[fa[u]] == (u))
#define isroot(u) (!fa[u] || (ls[fa[u]] != (u) && rs[fa[u]] != (u)))
int Max(int A, int B){
return e[A].b > e[B].b ? A : B;
}
void upt(int u){
val[u] = Max(Max(val[ls[u]], val[rs[u]]), num[u]);
}
void pushdown(int u){
if(!rev[u]) return;
swap(ls[u], rs[u]);
if(ls[u]) rev[ls[u]] ^= 1;
if(rs[u]) rev[rs[u]] ^= 1;
rev[u] = 0;
}
void rotate(int u){
int v = fa[u], w = fa[v], b = which(u) ? rs[u] : ls[u];
if(!isroot(v)) (which(v) ? ls[w] : rs[w]) = u;
which(u) ? (ls[v] = b, rs[u] = v) : (rs[v] = b, ls[u] = v);
fa[u] = w, fa[v] = u;
if(b) fa[b] = v;
upt(v);
}
void splay(int u){
static int stk[N], top;
stk[top = 1] = u;
while(!isroot(stk[top])) stk[top + 1] = fa[stk[top]], top++;
while(top) pushdown(stk[top--]);
while(!isroot(u)){
if(!isroot(fa[u])){
if(which(u) == which(fa[u])) rotate(fa[u]);
else rotate(u);
}
rotate(u);
}
upt(u);
}
void access(int u){
int v = 0;
while(u){
splay(u);
rs[u] = v;
v = u;
u = fa[u];
}
}
void makeroot(int u){
access(u);
splay(u);
rev[u] ^= 1;
}
int findroot(int u){
access(u);
splay(u);
while(pushdown(u), ls[u]) u = ls[u];
splay(u);
return u;
}
void link(int u, int v){
makeroot(u);
fa[u] = v;
}
void cut(int u, int v){
makeroot(u);
access(v);
splay(v);
ls[v] = fa[u] = 0;
upt(v);
}
void insert_edge(int i){
e[i].p = ++pcnt;
num[e[i].p] = val[e[i].p] = i;
link(e[i].u, e[i].p);
link(e[i].v, e[i].p);
}
void erase_edge(int i){
cut(e[i].u, e[i].p);
cut(e[i].v, e[i].p);
}
int query(int u, int v){
makeroot(u);
access(v);
splay(v);
return val[v];
}
int main(){
read(n), read(m), pcnt = n;
for(int i = 1; i <= m; i++)
read(e[i].u), read(e[i].v), read(e[i].a), read(e[i].b);
sort(e + 1, e + m + 1);
for(int i = 1; i <= m; i++){
if(findroot(e[i].u) != findroot(e[i].v)) insert_edge(i);
else{
int maxe = query(e[i].u, e[i].v);
if(e[maxe].b > e[i].b)
erase_edge(maxe), insert_edge(i);
}
if(findroot(1) == findroot(n))
ans = min(ans, e[i].a + e[query(1, n)].b);
}
write(ans < INF ? ans : -1), enter;
return 0;
}