Uva11770-lighting away

Question Link

A directed graph triggers a chain reaction for each node operation, so that the node and its direct or indirect points are marked, ask how many nodes need to be operated to mark all nodes

Idea: The strongly connected component of a directed graph. After the point is reduced by Tarjan, find the number of points with a degree of 0, that is, the answer. Same as uva11504.

Uva11504

Code:

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int MAXN = 10010;const int MAXM = 100010;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], dg[MAXN];int n, m;void init() {    tot = 0;    memset(head, -1, sizeof(head));}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 cas, t = 1;    scanf("%d", &cas);    while (cas--) {        scanf("%d%d", &n, &m);         init();        int u, v;        for (int i = 0; i < m; i++) {            scanf("%d%d", &u, &v);             addedge(u, v);        }         solve();         memset(dg, 0, sizeof(dg));        for (int u = 1; u <= n; u++) {            for (int i = head[u]; i != -1; i = edge[i].next) {                int v = edge[i].to;                if (Belong[u] != Belong[v]) {                    dg[Belong[v]]++;                  }              }         }         int ans = 0;        for (int i = 1; i <= scc; i++) {            if (dg[i] == 0)                 ans++;         }         printf("Case %d: %d\n", t++, ans);    }      return 0;}

Uva11770-lighting away