关于图连通性的几道题（水）

POJ 2186 强连通分量缩点

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 using namespace std;
 5
 6 int en[10010], col[10010], dfn[10010], low[10010], stack[10010], tot[10010], chu[10010];
 7 bool ins[10010];
 8 int n, m, esize, dtime, stop, scc;
 9 struct edge{
10     int v, n;
11 } e[50010];
12 void insert(int u, int v)
13 {
14     e[esize].v = v;
15     e[esize].n = en[u];
16     en[u] = esize ++;
17 }
18 void dfs(int x)
19 {
20     dfn[x] = low[x] = dtime ++;
21     stack[stop++] = x;
22     ins[x] = true;
23     for (int t = en[x]; t != -1; t = e[t].n){
24         int v = e[t].v;
25         if (!dfn[v]){
26             dfs(v);
27             low[x] = min(low[x], low[v]);
28         }
29         else if (ins[v]){
30             low[x] = min(low[x], dfn[v]);
31         }
32     }
33     if (dfn[x] == low[x]){
34         scc ++;
35         while(stack[--stop] != x){
36             col[stack[stop]] = scc;
37             ins[stack[stop]] = false;
38         }
39         col[x] = scc;
40         ins[x] = false;
41     }
42 }
43 int main()
44 {
45     scanf("%d %d", &n, &m);
46     int a, b;
47     esize = 0;
48     memset(en, -1, sizeof(en));
49     for (int i = 0; i < m; i++){
50         scanf("%d %d", &a, &b);
51         insert(a, b);
52     }
53     memset(dfn, 0, sizeof(dfn));
54     memset(col, 0, sizeof(col));
55     memset(ins, 0, sizeof(ins));
56     dtime = 1; stop = 0; scc = 0;
57     for (int i = 1; i <= n; i++)
58         if (!dfn[i]) dfs(i);
59     memset(chu, 0, sizeof(chu));
60     memset(tot, 0, sizeof(tot));
61     for (int i = 1; i <= n; i++){
62         int u = col[i];
63         tot[u]++;
64         for (int t = en[i]; t != -1; t = e[t].n){
65             int v = col[e[t].v];
66             if (u != v)
67                 chu[u] ++;
68         }
69     }
70     int cnt = 0, ans;
71     for (int i = 1; i <= scc; i++)
72         if (chu[i] == 0){
73             cnt ++;
74             ans = tot[i];
75         }
76     if (cnt > 1) ans = 0;
77     printf("%d\n", ans);
78     return 0;
79 }

POJ 1144 TOJ 1026 求割点数量

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<iostream>
 4 #include<cstdlib>
 5 #include<algorithm>
 6 using namespace std;
 7
 8 int esize, n, root, dtime;
 9 struct edge{
10     int v, n;
11 } e[100000];
12 int en[200], dfn[200], low[200];
13 bool cut[200];
14 int min(int a, int b)
15 {
16     if (a < b) return a; else return b;
17 }
18 void insert(int u, int v)
19 {
20     e[esize].v = v;
21     e[esize].n = en[u];
22     en[u] = esize++;
23 }
24 void dfs(int x, int fa)
25 {
26     int son = 0;
27     dfn[x] = low[x] = dtime++;
28     for (int t = en[x]; t != -1; t = e[t].n){
29         int v = e[t].v;
30         if (v == fa) continue;
31         if (!dfn[v]){
32             son++;
33             dfs(v, x);
34             low[x] = min(low[x], low[v]);
35             if ((x != root && low[v] >= dfn[x]) || (x == root && son > 1))
36                 cut[x] = true;
37         }
38         else{
39             low[x] = min(low[x], dfn[v]);
40         }
41     }
42 }
43 int main()
44 {
45     while(scanf("%d", &n) == 1 && n)
46     {
47         memset(en, -1, sizeof(en));
48         int x, y, esize = 0;
49         char ch;
50         while(scanf("%d", &x) == 1 && x){
51             while((ch = getchar()) != ‘\n‘){
52                 scanf("%d", &y);
53                 insert(x, y);
54                 insert(y, x);
55             }
56         }
57         memset(dfn, 0, sizeof(dfn));
58         memset(cut, 0, sizeof(cut));
59         root = 1; dtime = 1;
60         dfs(1, 0);
61         int ans = 0;
62         for (int i = 1; i <= n; i++)
63             if (cut[i]) {
64                 ans++;
65             }
66         printf("%d\n", ans);
67     }
68     return 0;
69 }

HDOJ 4738 无向图求桥

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 using namespace std;
 5
 6 const int inf = 2147483647;
 7 int esize, n, m, dtime, ans;
 8 int low[1010], dfn[1010], en[1010], f[1010];
 9 struct edge{
10     int v, n, w;
11     bool u;
12 } e[2002000];
13 int getf(int x)
14 {
15     if (x == f[x]) return x;
16     f[x] = getf(f[x]);
17     return f[x];
18 }
19 void unionxy(int x, int y)
20 {
21     int xroot = getf(x),
22         yroot = getf(y);
23     f[xroot] = yroot;
24 }
25 void insert(int u, int v, int w){
26     e[esize].v = v;
27     e[esize].n = en[u];
28     e[esize].w = w;
29     e[esize].u = false;
30     en[u] = esize ++;
31 }
32 void dfs(int u)
33 {
34     low[u] = dfn[u] = dtime ++;
35     for (int t = en[u]; t != -1; t = e[t].n){
36         if (e[t^1].u) continue;
37         e[t].u = true;
38         int v = e[t].v;
39         if (!dfn[v]){
40             dfs(v);
41             low[u] = min(low[u], low[v]);
42             if (low[v] > dfn[u]){
43                 if (e[t].w == 0)
44                     ans = min(ans, 1);
45                 else
46                     ans = min(ans, e[t].w);
47             }
48         }
49         else
50             low[u] = min(low[u], dfn[v]);
51     }
52 }
53 int main()
54 {
55     while(scanf("%d %d", &n, &m) && (n + m))
56     {
57         memset(en, -1, sizeof(en));
58         esize = 0;
59         for (int i = 1; i <= n; i++)
60             f[i] = i;
61         int x, y, w;
62         for (int i = 0; i < m; i++){
63             scanf("%d %d %d", &x, &y, &w);
64             insert(x, y, w);
65             insert(y, x, w);
66             unionxy(x, y);
67         }
68         int cnt = 0;
69         for (int i = 1; i <= n; i++)
70             if (f[i] == i) cnt ++;
71         if (cnt > 1){
72             puts("0");
73             continue;
74         }
75         memset(dfn, 0, sizeof(dfn));
76         dtime = 1, ans = inf;
77         for (int i = 1; i <= n; i++)
78             if (!dfn[i]) dfs(i);
79         if (ans == inf) ans = -1;
80         printf("%d\n", ans);
81     }
82     return 0;
83 }

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