利用Tarjan算法求最小公共祖先（LCA）

Author: Dev-XYS

Least-Common-Ancestor(Tarjan).cpp

@@ -0,0 +1,147 @@
+#include <cstdio>
+
+#define MAX_VERTEX_COUNT 100000
+#define MAX_EDGE_COUNT 100000
+
+using namespace std;
+
+struct vertex
+{
+	int first_edge;
+	bool finish;
+}V[MAX_VERTEX_COUNT];
+
+struct edge
+{
+	int endp, next;
+}E[MAX_EDGE_COUNT];
+
+int ec = 1;
+
+struct qvertex
+{
+	int first_edge;
+}QV[MAX_VERTEX_COUNT];
+
+struct qedge
+{
+	int endp, next, ans;
+}QE[MAX_EDGE_COUNT];
+
+int qec = 1;
+
+int fa[MAX_VERTEX_COUNT], size[MAX_VERTEX_COUNT], ancestor[MAX_VERTEX_COUNT];
+
+void add_edge(int u, int v)
+{
+	E[ec].next = V[u].first_edge;
+	V[u].first_edge = ec;
+	E[ec].endp = v;
+	ec++;
+}
+
+void add_qedge(int u, int v)
+{
+	QE[qec].next = QV[u].first_edge;
+	QV[u].first_edge = qec;
+	QE[qec].endp = v;
+	qec++;
+}
+
+void initial_set(int c)
+{
+	for (int i = 1; i <= c; i++)
+	{
+		fa[i] = i;
+		size[i] = 1;
+	}
+}
+
+int get_root(int x)
+{
+	if (fa[x] == x)
+	{
+		return x;
+	}
+	return (fa[x] = get_root(fa[x]));
+}
+
+void merge(int x, int y)
+{
+	int rtx = get_root(x), rty = get_root(y);
+	if (size[rtx] < size[rty])
+	{
+		fa[rtx] = rty;
+		size[rty] += size[rtx];
+	}
+	else
+	{
+		fa[rty] = rtx;
+		size[rtx] += size[rty];
+	}
+}
+
+void DFS(int u, int prev)
+{
+	fa[u] = u;
+	size[u] = 1;
+	ancestor[get_root(u)] = u;
+	
+	for (int cur = V[u].first_edge; cur != 0; cur = E[cur].next)
+	{
+		if (E[cur].endp != prev)
+		{
+			DFS(E[cur].endp, u);
+			merge(u, E[cur].endp);
+			ancestor[get_root(u)] = u;
+		}
+	}
+	V[u].finish = true;
+	
+	for (int cur = QV[u].first_edge; cur != 0; cur = QE[cur].next)
+	{
+		if (V[QE[cur].endp].finish == true)
+		{
+			QE[cur].ans = ancestor[get_root(QE[cur].endp)];
+		}
+	}
+}
+
+int main()
+{
+	int ivc, iqc;
+	scanf("%d%d", &ivc, &iqc);
+	
+	for (int i = 1; i < ivc; i++)
+	{
+		int u, v;
+		scanf("%d%d", &u, &v);
+		add_edge(u, v);
+		add_edge(v, u);
+	}
+	
+	for (int i = 0; i < iqc; i++)
+	{
+		int u, v;
+		scanf("%d%d", &u, &v);
+		add_qedge(u, v);
+		add_qedge(v, u);
+	}
+	
+	initial_set(ivc);
+	
+	DFS(1, 0);
+	
+	for (int i = 1; i <= ivc; i++)
+	{
+		for (int cur = QV[i].first_edge; cur != 0; cur = QE[cur].next)
+		{
+			if (QE[cur].ans != 0)
+			{
+				printf("The LCA of %d and %d is %d.\n", i, QE[cur].endp, QE[cur].ans);
+			}
+		}
+	}
+	
+	return 0;
+}