Uva247-calling circles (strongly connected component of a directed graph)

Question Link

A directed graph is given to identify all strongly connected components and output them.

Idea: Use the Tarjan algorithm for the strongly connected components of a directed graph and map the components to facilitate output. Pay attention to the output format.

Code:

#include <iostream>#include <cstdio>#include <cstring>#include <map>#include <algorithm>using namespace std;const int MAXN = 2000;const int MAXM = 50000;struct Edge{    int to, next;}edge[MAXM];int head[MAXN], tot;int Low[MAXN], DFN[MAXN], Stack[MAXN], Belong[MAXN];int Index, top;int scc;bool Instack[MAXN];int num[MAXN];int n, m, cnt;map<string, int> sTon;map<int, string> nTos; void init() {    tot = cnt = 0;    memset(head, -1, sizeof(head));    sTon.clear();    nTos.clear();}void addedge(int u, int v) {    edge[tot].to = v;    edge[tot].next = head[u];    head[u] = tot++;}void Tarjan(int u) {    int v;    Low[u] = DFN[u] = ++Index;    Stack[top++] = u;    Instack[u] = true;    for (int i = head[u]; i != -1; i = edge[i].next) {        v = edge[i].to;                 if (!DFN[v]) {            Tarjan(v);             if (Low[u] > Low[v]) Low[u] = Low[v];        }         else if (Instack[v] && Low[u] > DFN[v])             Low[u] = DFN[v];    }    if (Low[u] == DFN[u]) {        scc++;         do {             v = Stack[--top];             Instack[v] = false;            Belong[v] = scc;            num[scc]++;        } while (v != u);     }}void solve() {    memset(Low, 0, sizeof(Low));    memset(DFN, 0, sizeof(DFN));    memset(num, 0, sizeof(num));    memset(Belong, 0, sizeof(Belong));    memset(Stack, 0, sizeof(Stack));    memset(Instack, false, sizeof(Instack));    Index = scc = top = 0;    for (int i = 1; i <= n; i++)         if (!DFN[i])            Tarjan(i);}int main() {    int t = 0;    while (scanf("%d%d", &n, &m)) {        if (n == 0 && m == 0) break;         init();        string s1, s2;           for (int i = 0; i < m; i++) {            cin >> s1 >> s2;              if (sTon.find(s1) == sTon.end()) {                cnt++;                 sTon[s1] = cnt;                nTos[cnt] = s1;            }                 if (sTon.find(s2) == sTon.end()) {                cnt++;                 sTon[s2] = cnt;                nTos[cnt] = s2;            }                 addedge(sTon[s1], sTon[s2]);        }        if (t) printf("\n");          printf("Calling circles for data set %d:\n", ++t);        solve();        for (int i = 1; i <= scc; i++) {            int flag = 0;            for (int u = 1; u <= n; u++) {                if (Belong[u] == i) {                    if (!flag) {                        cout << nTos[u];                        flag = 1;                    }                    else cout << ", " << nTos[u];                }            }                          printf("\n");        }    }     return 0;}

Uva247-calling circles (strongly connected component of a directed graph)