最小生成树 : Kruskal

https://www.acwing.com/problem/content/861/
\(裸题\)

#include <iostream>                                                                           
#include <cstring>
#include <algorithm>
using namespace std;                                                                          
                                                                                              
const int N = 100010, M = 200010, INF = 0x3f3f3f3f;                                             
int n, m;                                                                                     
int p[N];                                                                                     
                                                                                              
struct Edge {                                                                                 
    int a, b, w;                                                                              
    bool operator< (const Edge &W)const {                                                     
        return w < W.w;                                                                       
    }                                                                                         
}edges[M];                                                                                    
                                                                                              
int find(int x) {                                                                             
    if (p[x] != x) p[x] = find(p[x]);                                                         
    return p[x];                                                                              
}                                                                                             
                                                                                              
int kruskal() {                                                                               
    sort(edges, edges + m);                                                                   
    for (int i = 1; i <= n; i++) p[i] = i;                                                    
    int res = 0, cnt = 0;                                                                     
    for (int i = 0; i < m; i++) {                                                             
        int a = edges[i].a, b = edges[i].b, w = edges[i].w;                                   
        a = find(a), b = find(b);                                                             
        if (a != b) {                                                                         
            p[a] = b;                                                                         
            res += w;                                                                         
            cnt++;                                                                            
        }                                                                                     
    }                                                                                         
    if (cnt < n - 1) return INF;                                                              
    return res;                                                                               
}

int main() {                                                                                  
    scanf("%d%d", &n, &m);                                                                    
    for (int i = 0; i < m; i++) {                                                             
        int a, b, c;                                                                          
        scanf("%d%d%d", &a, &b, &c);                                                          
        edges[i] = {a, b, c};                                                                 
    }                                                                                         
    int t = kruskal();                                                                        
    if (t == INF) puts("impossible");                                                         
    else printf("%d\n", t);                                                                   
    return 0;                                                                                 
}