Hihocoder recent public ancestor three online LCA

In the online LCA algorithm, DFS traverses the entire tree and inserts each vertex into the array when it appears, then, we can query the two vertices with the minimum Dep value between the last two vertices in the array and convert them to the rmq problem on the chain.

#include <cstdio>#include <cstring>#include <algorithm>#include <map>#include <set>#include <bitset>#include <queue>#include <stack>#include <string>#include <iostream>#include <cmath>#include <climits>using namespace std;const int maxn = 1e5 + 10;int head[maxn], nxt[maxn << 1], v[maxn << 1];int rpos[maxn], n, Q, cnt, ecnt;map<string, int> mp;map<int, string> smp;char name1[1024], name2[1024];struct Node {int dep, id;bool operator < (const Node &x) const {return dep < x.dep;}};Node val[maxn << 1], minv[maxn << 1][30];void adde(int uu, int vv) {v[ecnt] = vv; nxt[ecnt] = head[uu]; head[uu] = ecnt++;}int getid(char *str) {if(mp.count(str) == 0) {int mpz = mp.size();mp[str] = mpz + 1;smp[mpz + 1] = str;return mpz + 1;}return mp[str];}void dfs(int now, int fa, int dep) {val[++cnt].dep = dep; val[cnt].id = now;for(int i = head[now]; ~i; i = nxt[i]) if(v[i] != fa) {dfs(v[i], now, dep + 1);val[++cnt].dep = dep; val[cnt].id = now;}rpos[now] = cnt;}void initRMQ() {for(int i = 1; i <= cnt; i++) {minv[i][0] = val[i];}for(int j = 1; (1 << j) <= cnt; j++) {for(int i = 1; i + (1 << j) - 1 <= cnt; i++) {minv[i][j] = min(minv[i][j - 1], minv[i + (1 << (j - 1))][j - 1]);}}}Node query(int l, int r) {int k = 0;while((1 << (k + 1)) <= r - l + 1) k++;return min(minv[l][k], minv[r - (1 << k) + 1][k]);}int main() {memset(head, -1, sizeof(head));scanf("%d", &n);for(int i = 1; i <= n; i++) {scanf("%s%s", name1, name2);int a = getid(name1), b = getid(name2);adde(a, b); adde(b, a);}dfs(1, -1, 0);initRMQ();scanf("%d", &Q);while(Q--) {scanf("%s%s", name1, name2);int a = getid(name1), b = getid(name2);a = rpos[a]; b = rpos[b];if(a > b) swap(a, b);Node ret = query(a, b);puts(smp[ret.id].c_str());}return 0;}

　　

Hihocoder recent public ancestor three online LCA