51nod 1640 天气晴朗的魔法 最小生成树

题目链接：

题解：

#pragma comment(linker, "/STACK:102400000,102400000")
#include<cstdio>
#include<cstring>
#include<vector>
#include<algorithm>
#include<queue>
using namespace std;

typedef long long LL;
const int maxn = 2e5 + 10;

int n, m;
struct Edge {
int u, v, w;
}egs[maxn];

bool cmp1(const Edge& e1, const Edge& e2) {
return e1.w < e2.w;
}

bool cmp2(const Edge& e1, const Edge& e2) {
return e1.w > e2.w;
}

int fat[maxn];
int Find(int x) {
return fat[x] = fat[x] == x ? x : Find(fat[x]);
}

LL kruskal(int &ma,int sign) {
for (int i = 0; i <= n; i++) fat[i] = i;
LL ret = 0;
for (int i = 0; i < m; i++) {
int pu = Find(egs[i].u);
int pv = Find(egs[i].v);
if (pu != pv) {
if (sign) {
if (egs[i].w <= ma) {
ret += egs[i].w;
fat[pv] = pu;
}
}
else {
ma = max(ma, egs[i].w);
fat[pv] = pu;
}
}
}
return ret;
}

int main() {
while (scanf("%d%d", &n, &m) == 2 && n) {
int ma = -1;
for (int i = 0; i < m; i++) {
scanf("%d%d%d", &egs[i].u, &egs[i].v, &egs[i].w);
}
sort(egs, egs + m, cmp1);
kruskal(ma,0);
sort(egs, egs + m, cmp2);
LL ans = kruskal(ma,1);
printf("%lld\n", ans);
}
return 0;
}