【BestCoder】 HDOJ 5174 Ferries Wheel

注意只有一个轮子的时候要输出-1，不是n==1的时候输出-1.。。。

#include <iostream>
#include <queue> 
#include <stack> 
#include <map> 
#include <set> 
#include <bitset> 
#include <cstdio> 
#include <algorithm> 
#include <cstring> 
#include <climits>
#include <cstdlib>
#include <cmath>
#include <time.h>
#define maxn 200005
#define maxm 4005
#define eps 1e-7
#define mod 1000000007
#define INF 0x3f3f3f3f
#define PI (acos(-1.0))
#define lowbit(x) (x&(-x))
#define mp make_pair
#define ls o<<1
#define rs o<<1 | 1
#define lson o<<1, L, mid 
#define rson o<<1 | 1, mid+1, R
#define pii pair<int, int>
#pragma comment(linker, "/STACK:16777216")
typedef long long LL;
typedef unsigned long long ULL;
//typedef int LL;
using namespace std;
LL qpow(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base;base=base*base;b/=2;}return res;}
LL powmod(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base%mod;base=base*base%mod;b/=2;}return res;}
// head

struct node
{
	int u, v;
	ULL w;
}e[maxn];

int f[maxn];
ULL c[maxn];
ULL res1[maxn];
ULL res2[maxn];
int n;
ULL ans1;

int cmp1(node a, node b)
{
	return a.w < b.w;
}

int cmp2(node a, node b)
{
	return a.w > b.w;
}

int find(int u)
{
	return f[u] = u == f[u] ? f[u] : find(f[u]);
}

void merge1(int a, int b, ULL w)
{
	int aa = find(a), bb = find(b);
	if(aa != bb) {
		ULL t1 = c[aa] * c[bb] * w;
		f[bb] = aa;
		c[aa] += c[bb];
		ans1 += t1;
	}
}

void merge2(int a, int b, ULL w)
{
	int aa = find(a), bb = find(b);
	if(aa != bb) {
		ULL t1 = c[aa] * c[bb] * w;
		f[bb] = aa;
		c[aa] += c[bb];
		ans1 -= t1;
	}
}

void read()
{
	for(int i = 1; i < n; i++)
		scanf("%d%d%d", &e[i].u, &e[i].v, &e[i].w);
}

void work()
{
	for(int i = 0; i <= n; i++) c[i] = 1;
	for(int i = 0; i <= n; i++) f[i] = i;
	sort(e+1, e+n, cmp1);
	ans1 = 0;
	for(int i = 1; i < n; i++) merge1(e[i].u, e[i].v, e[i].w);

	for(int i = 0; i <= n; i++) c[i] = 1;
	for(int i = 0; i <= n; i++) f[i] = i;
	sort(e+1, e+n, cmp2);
	for(int i = 1; i < n; i++) merge2(e[i].u, e[i].v, e[i].w);
	cout << ans1 << endl;
}

int main()
{
	int _ = 0;
	while(scanf("%d", &n)!=EOF) {
		read();
		printf("Case #%d: ", ++_);
		work();
	}
	

	return 0;
}