Add Edge
Lesson 5 of 14 in Coddy's Graphs - Data Structures Series #9 course.
An edge connects two vertices. Since our graph is undirected, the connection goes both ways: if u and v are connected, then u appears in v's neighbor list and v appears in u's.
Before wiring anything, make sure both vertices exist by calling addVertex on each (it is a no-op if they already exist). Then push each one onto the other's neighbor list. Skip a duplicate push if the edge is already there. For a self-loop (u == v), add it only once.
Now let's write it.
Challenge
EasyAdd a method addEdge to the Graph class.
It takes two integers u and v and connects them in both directions:
- Make sure both
uandvexist (useaddVertexif not). - Add
vtou's neighbor list (only if it is not already there). - Add
utov's neighbor list (only if it is not already there). Ifu == v, do not add it a second time.
Try it yourself
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "graph.h"
static int _cmp_int(const void* a, const void* b) {
int ai = *(const int*)a, bi = *(const int*)b;
return (ai > bi) - (ai < bi);
}
int main() {
Graph g;
Graph_init(&g);
char line[1024];
while (fgets(line, sizeof(line), stdin)) {
line[strcspn(line, "\r\n")] = '\0';
char* cmd = strtok(line, " \t");
if (!cmd) continue;
if (strcmp(cmd, "verticesEmpty") == 0) { printf("%s\n", g.vertexCount == 0 ? "true" : "false"); }
if (strcmp(cmd, "hasVertex") == 0) { char* arg = strtok(NULL, " \t"); if (arg) printf("%s\n", Graph_indexOf(&g, atoi(arg)) != -1 ? "true" : "false"); }
if (strcmp(cmd, "addVertex") == 0) { char* arg = strtok(NULL, " \t"); if (arg) Graph_addVertex(&g, atoi(arg)); }
if (strcmp(cmd, "addEdge") == 0) { char* a1 = strtok(NULL, " \t"); char* a2 = strtok(NULL, " \t"); if (a1 && a2) Graph_addEdge(&g, atoi(a1), atoi(a2)); }
if (strcmp(cmd, "degree") == 0) {
char* arg = strtok(NULL, " \t");
if (arg) {
int k = atoi(arg);
int ki = Graph_indexOf(&g, k);
printf("%d\n", ki == -1 ? 0 : g.vertices[ki].n);
}
}
}
return 0;
}