【HDOJ】2988 Dark roads

最小生成树。

/*  */
#include <iostream>
#include <string>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <vector>
#include <deque>
#include <algorithm>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <climits>
#include <cctype>
#include <cassert>
using namespace std;

#define rep(i, a, n)     for (int i=a;i<n;++i)
#define per(i, a, n)     for (int i=n-1;i>=a;--i)
#define pb                 push_back
#define mp                 make_pair
#define all(x)             (x).begin(),(x).end()
#define SZ(x)             ((int)(x).size())
#define lson            l, mid, rt<<1
#define rson            mid+1, r, rt<<1|1

typedef struct Edge_t {
    int u, v, w;
    friend bool operator <(const Edge_t &a, const Edge_t &b) {
        return a.w < b.w;
    }
} Edge_t;

const int maxn = 200005;
int pre[maxn];
Edge_t E[maxn];

int find(int x) {
    if (x == pre[x])
        return x;
    return pre[x] = find(pre[x]);
}

int main() {
    int i, j, k;
    int n, m;
    int ans;
    int fu, fv;
    
    #ifndef ONLINE_JUDGE
        freopen("data.in", "r", stdin);
        freopen("data.out", "w", stdout);
    #endif
    
    while (scanf("%d %d", &n, &m)!=EOF && (n||m)) {
        for (i=0; i<n; ++i)
            pre[i] = i;
        for (i=0; i<m; ++i)
            scanf("%d %d %d", &E[i].u, &E[i].v, &E[i].w);
        sort(E, E+m);
        ans = 0;
        for (i=0; i<m; ++i) {
            fu = find(E[i].u);
            fv = find(E[i].v);
            if (fu != fv)
                pre[fu] = fv;
            else
                ans += E[i].w;
        }
        printf("%d
", ans);
    }
    
    #ifndef ONLINE_JUDGE
        printf("time = %d.
", (int)clock());
    #endif
    
    return 0;
}