uva-796.critical links(连通图的桥)

本题大意:求出一个无向图的桥的个数并且按照顺序输出所有桥.

本题思路:注意判重就行了,就是一个桥的裸题.

　　判重思路目前知道的有两种,第一种是哈希判重,第二种和邻接矩阵的优化一样,就是只存图的上半角或者下半角.

 

参考代码:

  1 /*************************************************************************
  2     > File Name: uva-796.critical_links.cpp
  3     > Author: CruelKing
  4     > Mail: 2016586625@qq.com 
  5     > Created Time: 2019年09月06日 星期五 15时58分54秒
  6     本题思路:注意边的判重.
  7  ************************************************************************/
  8 
  9 #include <cstdio>
 10 #include <cstring>
 11 #include <vector>
 12 #include <map>
 13 #include <algorithm>
 14 using namespace std;
 15 
 16 const int maxn = 10000 + 5, maxm = maxn * maxn + 5;
 17 int n;
 18 struct Edge {
 19     int to, next;
 20     bool cut;
 21 } edge[maxm];
 22 int head[maxn], tot;
 23 int low[maxn], dfn[maxn],stack[maxn];
 24 int Index, top, bridge;
 25 bool instack[maxn];
 26 bool cut[maxn];
 27 int add_block[maxn];
 28 
 29 void addedge(int u, int v) {
 30     edge[tot].to = v; edge[tot].next = head[u]; edge[tot].cut = false;
 31     head[u] = tot ++;
 32 }
 33 
 34 void init() {
 35     memset(head, -1, sizeof head);
 36     tot = 0;
 37 }
 38 
 39 map<int, int> mp;
 40 vector <pair<int, int> > ans;
 41 
 42 void tarjan(int u, int pre) {
 43     int v;
 44     low[u] = dfn[u] = ++ Index;
 45     instack[u] = true;
 46     int son = 0;
 47     int pre_cnt = 0;
 48     for(int i = head[u]; ~i; i = edge[i].next) {
 49         v = edge[i].to;
 50         if(v == pre && pre_cnt == 0) {
 51             pre_cnt ++;
 52             continue;
 53         }
 54         if(!dfn[v]) {
 55             son ++;
 56             tarjan(v, u);
 57             if(low[u] > low[v]) low[u] = low[v];
 58             if(low[v] > dfn[u]) {
 59                 bridge ++;
 60                 edge[i].cut = true;
 61                 edge[i ^ 1].cut = true;
 62             }
 63             if(u != pre && low[v] >= dfn[u]) {
 64                 cut[u] = true;
 65                 add_block[u] ++;
 66             }
 67         } else if(low[u] > dfn[v]) low[u] = dfn[v];
 68     }
 69     if(u == pre && son > 1) cut[u] = true;
 70     if(u == pre) add_block[u] = son - 1;
 71     instack[u] = false;
 72     top --;
 73 }
 74 
 75 void solve() {
 76     memset(dfn, 0, sizeof dfn);
 77     memset(instack, false, sizeof instack);
 78     memset(add_block, 0, sizeof add_block);
 79     memset(cut, false, sizeof cut);
 80     Index = top = bridge = 0;
 81     ans.clear();
 82     for(int i = 0; i < n; i ++)
 83         if(!dfn[i])
 84             tarjan(i, i);
 85     printf("%d critical links\n", bridge);
 86     for(int u = 0; u < n; u ++) {
 87         for(int i = head[u]; ~i; i = edge[i].next) {
 88             if(edge[i].cut && edge[i].to > u) ans.push_back(make_pair(u, edge[i].to));
 89         }
 90     }
 91     sort(ans.begin(), ans.end());
 92     for(int i = 0; i < ans.size(); i ++)
 93         printf("%d - %d\n", ans[i].first, ans[i].second);
 94     printf("\n");
 95 }
 96 
 97 inline bool ishash(int u, int v) {
 98     return !(mp[u * maxn + v]++ || mp[v * maxn + u]++);
 99 }
100 
101 int main() {
102     int u, num, v;
103     while(scanf("%d", &n) == 1) {
104         mp.clear();
105         init();
106         for(int i = 0; i < n; i ++) {
107             scanf("%d (%d)", &u, &num);
108             for(int i = 0; i < num; i ++) {
109                 scanf("%d", &v);
110                 if(ishash(u, v)) continue;
111                 addedge(u, v);
112                 addedge(v, u);
113             }
114         }
115         solve();
116     }
117     return 0;
118 }

 

posted @ 2019-09-06 16:57  Cruel_King  阅读(202)  评论(0)  编辑  收藏  举报