[算法] kruskal最小生成树算法

#include <stdio.h>
#include <stdlib.h>

#define MAX 100

int N, M;

struct Edge {
    int u,v;
    int weight;    
} edge[MAX];

int vertexs[MAX];
int parents[MAX];

int edge_cmp(const void* a, const void* b) {
    return ((struct Edge*)a)->weight - ((struct Edge*)b)->weight;  
}

int parents_find(int x) {
    int s;    
    for(s = x; parents[s] >= 0; s = parents[s]){
        ;     
    }
    return s;
}

void parents_union(int r1, int r2) {
    int s1, s2;
    int tmp;
    s1 = parents_find(r1);
    s2 = parents_find(r2);      
    tmp = parents[s1] + parents[s2];
    if(parents[s1] < parents[s2]) {
        parents[s2] = s1;     
        parents[s1] = tmp;
    }
    else {
        parents[s1] = s2;
        parents[s2] = tmp;     
    }
}

void kruskal() {
    int sum_weight = 0;
    int num = 0;
    int i, u, v;
    for(i = 0; i < M; i++) {
        u = edge[i].u;
        v = edge[i].v;
        if(parents_find(u) != parents_find(v)) {
            printf("%d %d %d\n", u + 1, v + 1, edge[i].weight);
            num ++;
            sum_weight += edge[i].weight;     
            parents_union(parents_find(u), parents_find(v));
        }
        if(num == N -1) {
            break;     
        }
    }
    printf("weight of MST is %d\n", sum_weight);
}

int main() {
    int i;
    int u, v, w;
     
    while(1) {
        scanf("%d%d", &N, &M);
        if(N == 0 && M == 0) {
            break;     
        } 
        /* init */
        for(i = 0; i < N; i++) {
            vertexs[i] = i;    
            parents[i] = -1;
        }

        for(i = 0; i < M; i++) {
            scanf("%d%d%d", &u, &v, &w);      
            u --;
            v --;
            edge[i].u = u;
            edge[i].v = v;
            edge[i].weight = w;
        }
        
        /* sort */
        qsort(edge, M, sizeof(edge[0]), edge_cmp);
        kruskal();
    } 

    return 0;
}

 

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