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;  //

const ll nmos = 0x80000000;  //-2147483648

const int inf = 0x3f3f3f3f;

template<typename T>

inline T read(T&x){

    x=;int f=;char ch=getchar();

    while (ch<''||ch>'') f|=(ch=='-'),ch=getchar();

    while (ch>=''&&ch<='') x=x*+ch-'',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 = ;

                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[];

                int sum,sec_tree;

                vector<int>g[];

                int len[][];

                int find(int x){

                    if(fa[x]==x)return x;

                    else return fa[x] = find(fa[x]);

                }

                void kruskal(){

                    for(int i=; i<=n; i++){

                        fa[i] = i;

                        g[i].clear();

                        g[i].pb(i);

                    }

                    sort(e+,e++m,cmp);

                    sum = ;

                    int k=;

                    for(int i=; i<=m; i++){

                        if(k==n-)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=; j<len1; j++){

                                for(int t=; 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[];

                            for(int j=; j<len1; j++){

                                tmp[j] = g[fx][j];

                            }

                            for(int j=; j<len2; j++){

                                g[fx].pb(g[fy][j]);

                            }

                            for(int j=; j<len1; j++){

                                g[fy].pb(tmp[j]);

                            }

                        }

                    }

                    sec_tree = inf;

                    for(int i=; 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 = ; T <= t_t;T++){

                printf("Case #%d : ", T);

                memset(len,,sizeof(len));

                scanf("%d%d", &n, &m);

                for(int i=; i<=m; i++){

                    scanf("%d%d%d", &e[i].u, &e[i].v, &e[i].c);

                    e[i].vis = false;

                }

                kruskal();

                int flag =;

                for(int i=; i<=n; i++){

                    if(find(i) != find()){

                        puts("No way");

                        flag = ;

                        break;

                    }

                }

                if(flag == ) continue;

                if(sec_tree<inf){

                    printf("%d\n",sec_tree);

                }

                else printf("No second way\n");

            }

    return ;

}

UVA - 10462