add LCA

code/LCA.cpp

@@ -0,0 +1,28 @@
+// use union find
+// u : root
+// G : graph (children lists)
+// q : queries q.first[u] : set of v for asking (u, v), q.second miroir
+// f : union-find array, a : ancestor, c : colour (init false)
+void makeSet(int *C, int i) { C[i] = i; }
+void Tarjan(int u, VI G[], pair<VI*, VI*> q, int f[], int a[], bool c[]) {
+  makeSet(f,u);
+  a[u]=u;
+  for(int v : G[u]) { // for each children of us
+    Tarjan(v, G, q, f, a, c);
+    unite(f,u,v);
+    a[find(f,u)] = u;
+  }
+  c[u] = true;
+  for(VI* qu : {q.first, q.second})
+    for(int v : qu[u])
+      if(c[v])
+        cout<<"LCA("<<u<<','<<v<<")="<<a[find(f,v)]<<endl;
+}
+void test() {
+  VI G[6];
+  G[0].push_back(1); G[0].push_back(2); G[2].push_back(3); G[2].push_back(4); G[3].push_back(5);
+  VI q1[6], q2[6];
+  q1[3].push_back(2); q2[2].push_back(3);
+  int f[6]; int a[6]; bool c[6] = {0, 0, 0, 0, 0, 0};
+  Tarjan(0, G, make_pair(q1, q2), f, a, c);
+}

main.tex

@@ -186,6 +186,9 @@ Temps de cuisson : $O(n)$
 \subsection{Exact Cover}
 {\scriptsize\lstinputlisting{code/ExactCover.cpp}}
 
+\subsection{Lowest Common Ancestor}
+{\scriptsize\lstinputlisting{code/LCA.cpp}}
+
 \section{Structures de données}
 
 \subsection{Suffix arrays}