mst graph code example

Example 1: prims minimum spanning tree

import math
def empty_tree (n):
    lst = []
    for i in range(n):
        lst.append([0]*n)
    return lst
def min_extension (con,graph,n):
    min_weight = math.inf
    for i in con:
        for j in range(n):
            if j not in con and 0 < graph[i][j] < min_weight:
                min_weight = graph[i][j]
                v,w = i,j
    return v,w
            
def min_span(graph):
    con = [0]
    n = len(graph)
    tree = empty_tree(n)
    while len(con) < n :
        i ,j  = min_extension(con,graph,n)
        tree[i][j],tree[j][i] = graph[i][j], graph[j][i]
        con += [j]
    return tree

def find_weight_of_edges(graph):
    tree = min_span(graph)
    lst = []
    lst1 = []
    x = 0
    for i in tree:
        lst += i 
    for i in lst:
        if i not in lst1:
            lst1.append(i)
            x += i
    return x

graph = [[0,1,0,0,0,0,0,0,0],
         [1,0,3,4,0,3,0,0,0],
         [0,3,0,0,0,4,0,0,0],
         [0,4,0,0,2,9,1,0,0],
         [0,0,0,2,0,6,0,0,0],
         [0,3,4,9,6,0,0,0,6],
         [0,0,0,1,0,0,0,2,8],
         [0,0,0,0,0,0,2,0,3],
         [0,0,0,0,0,6,8,3,0]]
graph1 = [[0,3,5,0,0,6],
          [3,0,4,1,0,0],
          [5,4,0,4,5,2],
          [0,1,4,0,6,0],
          [0,0,5,6,0,8],
          [6,0,2,0,8,0]]
print(min_span(graph1))
print("Total weight of the tree is: " + str(find_weight_of_edges(graph1)))

Example 2: find the graph is minimal spanig tree or not

#include <iostream>
#include <vector>
#include <utility>
#include <algorithm>

using namespace std;
const int MAX = 1e4 + 5;
int id[MAX], nodes, edges;
pair <long long, pair<int, int> > p[MAX];

void initialize()
{
    for(int i = 0;i < MAX;++i)
        id[i] = i;
}

int root(int x)
{
    while(id[x] != x)
    {
        id[x] = id[id[x]];
        x = id[x];
    }
    return x;
}

void union1(int x, int y)
{
    int p = root(x);
    int q = root(y);
    id[p] = id[q];
}

long long kruskal(pair<long long, pair<int, int> > p[])
{
    int x, y;
    long long cost, minimumCost = 0;
    for(int i = 0;i < edges;++i)
    {
        // Selecting edges one by one in increasing order from the beginning
        x = p[i].second.first;
        y = p[i].second.second;
        cost = p[i].first;
        // Check if the selected edge is creating a cycle or not
        if(root(x) != root(y))
        {
            minimumCost += cost;
            union1(x, y);
        }    
    }
    return minimumCost;
}

int main()
{
    int x, y;
    long long weight, cost, minimumCost;
    initialize();
    cin >> nodes >> edges;
    for(int i = 0;i < edges;++i)
    {
        cin >> x >> y >> weight;
        p[i] = make_pair(weight, make_pair(x, y));
    }
    // Sort the edges in the ascending order
    sort(p, p + edges);
    minimumCost = kruskal(p);
    cout << minimumCost << endl;
    return 0;
}