UVA11504- Dominos(Tarjan+縮點)，dominostarjan

UVA11504- Dominos(Tarjan+縮點)，dominostarjan

題目連結

題意：多米諾骨牌的遊戲，給出一些牌，以及哪張牌倒了之後會推倒哪張牌，求最少的推倒牌的張數，使得所有牌都倒下去。

思路：有向圖的強連通分量，用Tarjan縮點之後找出入度為0的點的個數，即為答案。

代碼：

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int MAXN = 100100;const int MAXM = 100100;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 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(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;    scanf("%d", &cas);    while (cas--) {        init();        scanf("%d%d", &n, &m);                 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 (Low[u] != Low[v])                     dg[Belong[v]]++;            }         }        int ans = 0;        for (int i = 1; i <= scc; i++)            if (dg[i] == 0)                ans++;        printf("%d\n", ans);    }    return 0;}