/*Kruskal算法
1:将所有邊按照從小到大的順序排列
2:依次将權值最小的邊加入生成樹的子集當中
3:重複以上的步驟直到找出n-1條邊為止
注:Kruskal适合求稀疏圖問題,而prim算法适合求稠密圖問題
*/
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
using namespace std;
const int maxn = + ;
int n, m, parent[maxn], childNum[maxn], sum;
struct Edge {
int u, v, val;
} edge[maxn];
vector<Edge> ans;
bool cmp(const Edge & s1, const Edge & s2) {
return s1.val < s2.val;
}
int UFind(int u) {
return parent[u] == u ? u : UFind(parent[u]);
}
bool join(int u, int v) {
int root1 = UFind(u);
int root2 = UFind(v);
if(root1 == root2) return false; //存在環
if(childNum[root1] > childNum[root2]) { //将節點數少的點連接配接到節點數量多的樹上面
parent[root2] = root1;
childNum[root1] += childNum[root2];
}
else {
parent[root1] = root2;
childNum[root2] += childNum[root1];
}
}
bool kruskal() {
sort(edge, edge + m, cmp);
int sideNum = ; //邊的個數
for(int i = ; i < m; i++) {
if(join(edge[i].u, edge[i].v)) {
sideNum++;
sum += edge[i].val;
ans.push_back(edge[i]);
}
if(sideNum == n - ) return true; //如果邊的個數到達n-1條,則最小生成樹的建構完成
}
return false;
}
int main()
{
cout << "enter the number of vertexes and sides:" << endl;
cin >> n >> m;
for(int i = ; i < n; i++) { //初始化
parent[i] = i;
childNum[i] = ;
}
sum = ;
for(int i = ; i < m; i++)
cin >> edge[i].u >> edge[i].v >> edge[i].val;
ans.clear();
if(kruskal()) {
cout << "kruskal path:" << endl;
for(int i = ; i < ans.size(); i++) cout << ans[i].u << "->" << ans[i].v << endl;
cout << "the sum is:" << endl;
cout << sum << endl;
}
else
cout << "error" << endl;
return ;
}