题目链接
题解
完了我连(kruskal)裸题都做不出来了。。
题目是求最小树形图，即有向图最小生成树
我们不能直接上(kruskal)，而要保证先加入前面的点，
所以我们排序的时候第一关键字改为高度即可
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<map>
#define Redge(u) for (int k = h[u],to; k; k = ed[k].nxt)
#define REP(i,n) for (int i = 1; i <= (n); i++)
#define mp(a,b) make_pair<int,int>(a,b)
#define cls(s) memset(s,0,sizeof(s))
#define cp pair<int,int>
#define LL long long int
using namespace std;
const int maxn = 1000005,maxm = 2000005,INF = 1000000000;
inline int read(){
int out = 0,flag = 1; char c = getchar();
while (c < 48 || c > 57){if (c == '-') flag = -1; c = getchar();}
while (c >= 48 && c <= 57){out = (out << 3) + (out << 1) + c - 48; c = getchar();}
return out * flag;
}
int high[maxn],n,m;
int h[maxn],ne;
struct EDGE{int from,to,nxt; LL w;}ed[maxm];
inline void build(int u,int v,LL w){
ed[++ne] = (EDGE){u,v,h[u],w}; h[u] = ne;
}
int tot;
struct edge{int a,b; LL w;}e[maxm];
inline bool operator <(const edge& a,const edge& b){
return high[a.b] == high[b.b] ? a.w < b.w : high[a.b] > high[b.b];
}
int vis[maxn],q[maxn],head,tail,N;
void bfs(){
q[head = tail = 0] = 1; vis[1] = true; N = 1;
int u;
while (head <= tail){
u = q[head++];
Redge(u) if (!vis[to = ed[k].to]){
N++; vis[to] = true; q[++tail] = to;
}
}
}
int pre[maxn];
int find(int u){return u == pre[u] ? u : pre[u] = find(pre[u]);}
void kruskal(){
for (int i = 1; i <= n; i++) pre[i] = i;
LL ans = 0; int cnt = N,fa,fb;
sort(e + 1,e + 1 + tot);
for (int i = 1; i <= tot && cnt > 1; i++){
fa = find(e[i].a); fb = find(e[i].b);
if (fa != fb){
pre[fb] = fa;
cnt--;
ans += e[i].w;
}
}
printf("%d %lld
",N,ans);
}
int main(){
n = read(); m = read();
for (int i = 1; i <= n; i++) high[i] = read();
int a,b,w;
for (int i = 1; i <= m; i++){
a = read(); b = read(); w = read();
if (high[a] >= high[b]) build(a,b,w);
if (high[b] >= high[a]) build(b,a,w);
}
bfs();
for (int i = 1; i <= ne; i++){
if (vis[ed[i].from] && vis[ed[i].to])
e[++tot] = (edge){ed[i].from,ed[i].to,ed[i].w};
}
kruskal();
return 0;
}