Add Vertex
Lesson 4 of 14 in Coddy's Graphs - Data Structures Series #9 course.
A vertex is a single point in the graph. Adding one means registering its key in the vertices map with an empty neighbor list: it exists, but has no connections yet.
If the key is already in the map, do nothing. We do not want to wipe out a vertex's existing neighbors just because someone called addVertex on it twice. That kind of idempotent behavior makes the method safe to call from addEdge later.
Let's write it.
Challenge
EasyAdd a method addVertex to the Graph class.
It takes an integer key and:
- If
keyis not invertices, add it with an empty neighbor list. - If
keyis already invertices, do nothing.
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)); }
}
return 0;
}