UVA - 10462-Is There A Second Way Left? Kruskal求次小生成树

UVA - 10462 

 

题意： 求次小生成树的模板题，这道题因为有重边的存在，所以用kruskal求比较好。

 

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <cstdlib>
#include <iterator>
#include <cmath>
#include <iomanip>
#include <bitset>
#include <cctype>
using namespace std;
//#pragma comment(linker, "/STACK:102400000,102400000")  //c++
#define lson (l , mid , rt << 1)
#define rson (mid + 1 , r , rt << 1 | 1)
#define debug(x) cerr << #x << " = " << x << "\n";
#define pb push_back
#define pq priority_queue

typedef long long ll;
typedef unsigned long long ull;

typedef pair<ll ,ll > pll;
typedef pair<int ,int > pii;

//priority_queue<int> q;//这是一个大根堆q
//priority_queue<int,vector<int>,greater<int> >q;//这是一个小根堆q
#define fi first
#define se second
#define endl '\n'

#define OKC ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define FT(A,B,C) for(int A=B;A <= C;++A)  //用来压行
#define REP(i , j , k)  for(int i = j ; i <  k ; ++i)
//priority_queue<int ,vector<int>, greater<int> >que;

const ll mos = 0x7FFFFFFF;  //2147483647
const ll nmos = 0x80000000;  //-2147483648
const int inf = 0x3f3f3f3f;

template<typename T>
inline T read(T&x){
    x=0;int f=0;char ch=getchar();
    while (ch<'0'||ch>'9') f|=(ch=='-'),ch=getchar();
    while (ch>='0'&&ch<='9') x=x*10+ch-'0',ch=getchar();
    return x=f?-x:x;
}
// #define _DEBUG;         //*//
#ifdef _DEBUG
freopen("input", "r", stdin);
// freopen("output.txt", "w", stdout);
#endif
/*-----------------show time----------------*/
                const int maxn = 300;
                int n,m;
                struct node
                {
                    int u,v;
                    int c;
                    bool vis;
                }e[maxn];

                bool cmp(node a,node b){
                    return  a.c < b.c;
                }
                int fa[200];
                int sum,sec_tree;
                vector<int>g[200];
                int len[200][200];
                int find(int x){
                    if(fa[x]==x)return x;
                    else return fa[x] = find(fa[x]);
                }
                void kruskal(){

                    for(int i=1; i<=n; i++){
                        fa[i] = i;
                        g[i].clear();
                        g[i].pb(i);
                    }

                    sort(e+1,e+1+m,cmp);
                    sum = 0;
                    int k=0;
                    for(int i=1; i<=m; i++){
                        if(k==n-1)break;

                        int fx = find(e[i].u);
                        int fy = find(e[i].v);
                        
                        if(fx!=fy){
                            sum += e[i].c;

                            k++;
                            e[i].vis = true;

                            int len1 = g[fx].size();
                            int len2 = g[fy].size();

                            for(int j=0; j<len1; j++){
                                for(int t=0; t<len2; t++){
                                    len[g[fx][j]][g[fy][t]] = len[g[fy][t]][g[fx][j]] = e[i].c;
                                }
                            }

                            fa[fy] = fx;

                            int tmp[110];

                            for(int j=0; j<len1; j++){
                                tmp[j] = g[fx][j];
                            }
                            for(int j=0; j<len2; j++){
                                g[fx].pb(g[fy][j]);
                            }
                            for(int j=0; j<len1; j++){
                                g[fy].pb(tmp[j]);
                            }
                        }
                    }

                    sec_tree = inf;
                    for(int i=1; i<=m; i++){
                        if(e[i].vis==false){
                            sec_tree = min(sec_tree, sum - len[e[i].u][e[i].v] + e[i].c);
                        }

                    }
                    // debug(sec_tree);
                }
int main(){
            int t_t;
            scanf("%d", &t_t);
            for(int T = 1; T <= t_t;T++){
                printf("Case #%d : ", T);
                memset(len,0,sizeof(len));
                scanf("%d%d", &n, &m);
                for(int i=1; i<=m; i++){
                    scanf("%d%d%d", &e[i].u, &e[i].v, &e[i].c);
                    e[i].vis = false;
                }
                kruskal();
                int flag =1;
                for(int i=1; i<=n; i++){
                    if(find(i) != find(1)){
                        puts("No way");
                        flag = 0;
                        break;
                    }
                }
                if(flag == 0) continue;
                if(sec_tree<inf){
                    printf("%d\n",sec_tree);
                }
                else printf("No second way\n");
            }        
    return 0;
}