最小生成树C代码实例

在贪婪算法这一章提到了最小生成树的一些算法，首先是Kruskal算法，实现如下：

MST.h

#ifndef H_MST#define H_MST#define NODE node *#define G graph *#define MST edge **/* the undirect graph start */typedef struct _node {char data;int flag;struct _node *parent;} node;typedef struct _edge {node *A;node *B;int w;} edge;typedef struct _graph {node **nodelist;int nodeLen;edge **edgelist;int edgeLen;} graph;/* the undirect graph end */int kruskal(G , edge *[]);int makeset(NODE);int find(NODE , NODE);int merge(NODE , NODE);int comp(const void *, const void *);#endif

MST.c

#include "mst.h"#include <stdlib.h>#include <stdio.h>int main(int argc, char *argv[]){/* Construct the undirect connected graph */graph g;g.nodeLen = 6;g.edgeLen = 10;node node_a, node_b, node_c, node_d, node_e, node_f;edge edge_1, edge_2, edge_3, edge_4, edge_5, edge_6, edge_7, edge_8, edge_9, edge_10;node_a.data = 'a';node_a.flag = 0;node_a.parent = (node *)malloc(sizeof(node));node_b.data = 'b';node_b.flag = 0;node_b.parent = (node *)malloc(sizeof(node));node_c.data = 'c';node_c.flag = 0;node_c.parent = (node *)malloc(sizeof(node));node_d.data = 'd';node_d.flag = 0;node_d.parent = (node *)malloc(sizeof(node));node_e.data = 'e';node_e.flag = 0;node_e.parent = (node *)malloc(sizeof(node));node_f.data = 'f';node_f.flag = 0;node_f.parent = (node *)malloc(sizeof(node));edge_1.A = &node_a;edge_1.B = &node_b;edge_1.w = 5;edge_2.A = &node_a;edge_2.B = &node_c;edge_2.w = 6;edge_3.A = &node_a;edge_3.B = &node_d;edge_3.w = 4;edge_4.A = &node_b;edge_4.B = &node_c;edge_4.w = 1;edge_5.A = &node_b;edge_5.B = &node_d;edge_5.w = 2;edge_6.A = &node_c;edge_6.B = &node_d;edge_6.w = 2;edge_7.A = &node_c;edge_7.B = &node_e;edge_7.w = 5;edge_8.A = &node_c;edge_8.B = &node_f;edge_8.w = 3;edge_9.A = &node_d;edge_9.B = &node_f;edge_9.w = 4;edge_10.A = &node_e;edge_10.B = &node_f;edge_10.w = 4;node **nodelist;nodelist = (node **)malloc(sizeof(node *) * g.nodeLen);edge **edgelist;edgelist = (edge **)malloc(sizeof(edge *) * g.edgeLen);nodelist[0] = &node_a;nodelist[1] = &node_b;nodelist[2] = &node_c;nodelist[3] = &node_d;nodelist[4] = &node_e;nodelist[5] = &node_f;edgelist[0] = &edge_1;edgelist[1] = &edge_2;edgelist[2] = &edge_3;edgelist[3] = &edge_4;edgelist[4] = &edge_5;edgelist[5] = &edge_6;edgelist[6] = &edge_7;edgelist[7] = &edge_8;edgelist[8] = &edge_9;edgelist[9] = &edge_10;g.nodelist = nodelist;g.edgelist = edgelist;edge *X[g.nodeLen-1];int e = 0;while (e < g.edgeLen){printf("%c-%c %d\n", g.edgelist[e]->A->data, g.edgelist[e]->B->data, g.edgelist[e]->w);e++;}printf("------------------------------------------------------\n");kruskal(&g, X);e = 0;while (e < (g.nodeLen-1)){printf("%c-%c %d\n", X[e]->A->data, X[e]->B->data, X[e]->w);e++;}}int kruskal(G g, edge *pX[]){int i, j;/* Initially every disjoint set have one node */for (i = 0; i < g->nodeLen; i++)makeset(g->nodelist[i]);/* sort the edgelist */qsort(g->edgelist, g->edgeLen, sizeof(edge *), comp);int e = 0;while (e < g->edgeLen){printf("%c-%c %d\n", g->edgelist[e]->A->data, g->edgelist[e]->B->data, g->edgelist[e]->w);e++;}printf("------------------------------------------------------\n");node da, db;da.parent = (node *)malloc(sizeof(node));db.parent = (node *)malloc(sizeof(node));for (j = 0; j < g->edgeLen; j++){find(g->edgelist[j]->A, &da);find(g->edgelist[j]->B, &db);if (da.data != db.data){merge(g->edgelist[j]->A, g->edgelist[j]->B);*pX++ = g->edgelist[j];}}}int makeset(NODE n){n->parent = n;}int find(NODE n, NODE ds){if (n->parent == n){ds->data = n->data;ds->flag = 1;ds->parent = n->parent;}if (n->parent != n)find(n->parent, ds);}int merge(NODE da, NODE db){if (da->flag)db->parent = da;elseda->parent = db;}int comp(const void *ea, const void *eb){if ((*(edge **)ea)->w > (*(edge **)eb)->w) return 1;else if ((*(edge **)ea)->w == (*(edge **)eb)->w ) return 0;else return -1;}

在实现这个算法的时候，真正体会到了测试的重要性。程序能成功编译只是完成了一小部分，必须经过反复的测试才能发布。