洛谷P2387 [NOI2014]魔法森林(LCT)

一时失言乱红尘 2023-08-17 17:21 122阅读 0赞

# 魔法森林 #

[题目传送门][Link 1]

## 解题思路 ##

把每条路按照\\(a\\)的值从小到大排序。然后用LCT按照b的值维护最小生成树，将边按照顺序放入。如果\\(1\\)到\\(n\\)有了一条路径，就更新最小答案。这个过程就相当于枚举了每一个\\(a\\)作为最大的\\(a\\)，然后求出了其对应的最小\\(b\\)的最大值。

## 代码如下 ##

#include <bits/stdc++.h> using namespace std; typedef long long ll; const int N = 300005; int fa[N], ch[N][2], sta[N], maxx[N]; ll v[N]; bool rev[N]; inline bool get(int x) { return ch[fa[x]][1] == x; } inline bool is_root(int x) { return (!fa[x] || ch[fa[x]][1] != x && ch[fa[x]][0] != x); } inline void pushr(int x) { swap(ch[x][0], ch[x][1]); rev[x] ^= 1; } inline void push_up(int x) { int t = v[maxx[ch[x][1]]] > v[maxx[ch[x][0]]]? maxx[ch[x][1]]: maxx[ch[x][0]]; maxx[x] = v[t] > v[x]? t: x; } inline void push_down(int x) { if(rev[x]){ pushr(ch[x][0]); pushr(ch[x][1]); rev[x] = 0; } } inline void rotate(int x) { int y = fa[x], z = fa[y]; int u = get(x); ch[y][u] = ch[x][u^1], fa[ch[x][u^1]] = y; if(!is_root(y)) ch[z][get(y)] = x; fa[x] = z; ch[x][u^1] = y, fa[y] = x; push_up(y), push_up(x); } inline void splay(int x) { int pos = 0; sta[++pos] = x; for(int i = x; !is_root(i); i = fa[i]) sta[++pos] = fa[i]; while(pos) push_down(sta[pos--]); while(!is_root(x)){ int y = fa[x]; if(!is_root(y)) get(x) == get(y)? rotate(y): rotate(x); rotate(x); } } inline void access(int x) { for(int y = 0; x; y = x, x = fa[x]) splay(x), ch[x][1] = y, push_up(x); } inline void make_root(int x) { access(x);splay(x); pushr(x); } inline void split(int x, int y) { make_root(x); access(y);splay(y); } inline int find_root(int x) { access(x);splay(x); while(ch[x][0]){ push_down(x); x = ch[x][0]; } splay(x); return x; } int a[N], b[N]; void link(int id) { make_root(a[id]); make_root(b[id]); fa[a[id]] = id; fa[b[id]] = id; } int main() { int n, m; scanf("%d%d", &n, &m); int line = 0; ll sum = 0; for(int i = n + 1; i <= n + m; i ++){ int x, y, z; scanf("%d%d%d", &x, &y, &z); a[i] = x, b[i] = y, v[i] = z; maxx[i] = i; make_root(x); if(find_root(y) != x){ link(i); ++line; sum += z; } else { split(x, y); int k = maxx[y]; if(v[k] > z){ splay(k); fa[ch[k][0]] = fa[ch[k][1]] = 0; ch[k][0] = ch[k][1] = 0; link(i); sum -= v[k] - z; } } } if(line == n - 1) printf("%lld\n", sum); else printf("orz\n"); return 0; }

转载于:https://www.cnblogs.com/whisperlzw/p/11404894.html

[Link 1]: https://www.luogu.org/problem/P2387