Poj1236-network of schools (Tarjan + indent)

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Test Instructions: given an undirected graph, ask at least a few points to traverse the full map, and add at least a few edges to make the graph a strongly connected graph.

Ideas: for the directed graph, first of all to find a few strong connected components, then each strong connected component contraction point, the formation of a DAG, the first sentence at the beginning of the question that the diagram is connected. Then, if you want to traverse the entire graph, just look for a few points with a 0 degree of entry and exit, and the number of edges to add depends on the degree of entry and exit of all points.

Code:

#include <iostream> #include <cstdio> #include <cstring> #include <vector> #include <stack > #include <algorithm>using namespace std;const int maxn = 105;vector<int> g[maxn];stack<int> s; int PRE[MAXN], LOWLINK[MAXN], SCCNO[MAXN], Dfs_clock, Scc_cnt;int N, In[maxn], out[maxn];void tarjan (int u) {Pre[u] =     Lowlink[u] = ++dfs_clock;    S.push (U);         for (int i = 0; i < g[u].size (); i++) {int v = g[u][i];             if (!pre[v]) {Tarjan (v);        Lowlink[u] = min (Lowlink[u], lowlink[v]);    } else if (!sccno[v]) lowlink[u] = min (Lowlink[u], pre[v]);         } if (lowlink[u] = = Pre[u]) {scc_cnt++;        int x =-1;             while (x! = u) {x = S.top ();            S.pop ();        SCCNO[X] = scc_cnt;    }}}void FIND_SCC () {memset (pre, 0, sizeof (pre));    memset (sccno, 0, sizeof (SCCNO));    memset (lowlink, 0, sizeof (lowlink));    Dfs_clock = scc_cnt = 0; for (int i = 1; I <= N; i++) if (!pre[i]) Tarjan (i);}        int main () {while (scanf ("%d", &n)! = EOF) {int u;            for (int i = 1; I <= n; i++) {g[i].clear ();        while (scanf ("%d", &u) && u) g[i].push_back (u);        } FIND_SCC ();             if (scc_cnt = = 1) {printf ("1\n0\n");        Continue             } else {memset (in, 0, sizeof (in));             memset (out, 0, sizeof (out)); for (int u = 1, u <= n; u++) {for (int i = 0; i < g[u].size (); i++) {int v = g[u                     ][i];                          if (sccno[u]! = Sccno[v]) {in[sccno[v]]++;                    out[sccno[u]]++;            }}} int a = 0, b = 0;                 for (int i = 1; I <= scc_cnt; i++) {if (in[i] = = 0) a++;              if (out[i]== 0) b++; } intAns = max (A, b);        printf ("%d\n%d\n", A, ans); }} return 0;}

Poj1236-network of schools (Tarjan + indent)