【算法】【树】最近公共祖先LCA——Tarjan算法

class LCA_problem {
public:
const static int N = 10000 + 10;
int parent
;
int ancester
;
vector<int> tree
;
vector<int> qes
;
bool isroot
;
bool visited
;
int n;
void init(int n) {
for (int i = 1; i <= n; i++) {
parent[i] = i;
isroot[i] = true;
ancester[i] = 0;
visited[i] = false;
qes[i].clear();
tree[i].clear();
}
}
int find(int u) {
if (u != parent[u]) {parent[u] = find(parent[u]); return parent[u];}
return u;
}
int union_(int x, int y) {
int p1 = find(x);
int p2 = find(y);
if (p1==p2) return 0;
parent[p1] = p2;
return 1;
}
void lca(int u) {   //模拟深度遍历，在遍历的过程中，回答查询问题；
ancester[u] = u;
int size = tree[u].size();
//printf("# %d %d\n", u, size);
for (int i = 0; i < size; i++) {

lca(tree[u][i]);
union_(u, tree[u][i]);
ancester[find(u)] = u;

}
visited[u] = true;
size = qes[u].size();
for (int i = 0;i < size; i++) {
if (visited[qes[u][i]]) {
printf("%d\n", ancester[find(qes[u][i])]);
return;
}
}
}
void solve() {
int test_num, start, end;
scanf("%d", &test_num);
for (int t = 0; t < test_num; t++) {
scanf("%d", &n);
init(n);
for (int i = 0;i < n-1; i++) {
scanf("%d%d", &start, &end);
tree[start].push_back(end);
isroot[end] = false;
}
scanf("%d%d", &start, &end);
qes[start].push_back(end);
qes[end].push_back(start);
for (int i = 1; i <= n; i++) {
if (isroot[i]) { lca(i); break; }
}
}
}
};