prims.c

#include <stdio.h>
#include <limits.h>

#define MAX_VERTICES 100
#define INF INT_MAX

int minKey(int key[], int mstSet[], int vertices) {
    int min = INF, min_index;

    for (int v = 0; v < vertices; v++) {
        if (mstSet[v] == 0 && key[v] < min) {
            min = key[v];
            min_index = v;
        }
    }

    return min_index;
}

void printMST(int parent[], int graph[MAX_VERTICES][MAX_VERTICES], int vertices) {
    printf("Edge \tWeight\n");
    for (int i = 1; i < vertices; i++) {
        printf("%d - %d \t%d \n", parent[i], i, graph[i][parent[i]]);
    }
}

void primMST(int graph[MAX_VERTICES][MAX_VERTICES], int vertices) {
    int parent[MAX_VERTICES];
    int key[MAX_VERTICES];
    int mstSet[MAX_VERTICES];

    for (int i = 0; i < vertices; i++) {
        key[i] = INF;
        mstSet[i] = 0;
    }

    key[0] = 0;
    parent[0] = -1;

    for (int count = 0; count < vertices - 1; count++) {
        int u = minKey(key, mstSet, vertices);

        mstSet[u] = 1;

        for (int v = 0; v < vertices; v++) {
            if (graph[u][v] && mstSet[v] == 0 && graph[u][v] < key[v]) {
                parent[v] = u;
                key[v] = graph[u][v];
            }
        }
    }

    printMST(parent, graph, vertices);
}

int main() {
    int vertices;

    printf("Enter the number of vertices: ");
    scanf("%d", &vertices);

    int graph[MAX_VERTICES][MAX_VERTICES];
    printf("Enter the adjacency matrix (enter 0 if there is no edge):\n");
    for (int i = 0; i < vertices; i++) {
        for (int j = 0; j < vertices; j++) {
            scanf("%d", &graph[i][j]);
            if (graph[i][j] == 0 && i != j) {
                graph[i][j] = INF;
            }
        }
    }

    primMST(graph, vertices);

    return 0;
}