【hihoCoder第十五周】最近公共祖先·二

  1 #include <bits/stdc++.h>
  2 using namespace std;
  3 
  4 const int MAXN = 1000010;
  5 int rmq[2 * MAXN]; //rmq数组，就是欧拉序列对应的深度序列
  6 
  7 struct ST {
  8     int mm[2 * MAXN];
  9     int dp[2 * MAXN][20]; //最小值对应的下标
 10     void init(int n) {
 11         mm[0] = -1;
 12         for(int i = 1; i <= n; i++) {
 13             mm[i] = ((i & (i - 1)) == 0) ? mm[i - 1] + 1 : mm[i - 1];
 14             dp[i][0] = i;
 15         }
 16         for(int j = 1; j <= mm[n]; j++)
 17             for(int i = 1; i + (1 << j) - 1 <= n; i++)
 18                 dp[i][j] = rmq[dp[i][j - 1]] <
 19                            rmq[dp[i + (1 << (j - 1))][j - 1]] ? dp[i][j - 1] : dp[i + (1 << (j - 1))][j - 1];
 20     }
 21     int query(int a, int b) { //查询[a,b]之间最小值的下标
 22         if(a > b)swap(a, b);
 23         int k = mm[b - a + 1];
 24         return rmq[dp[a][k]] <=
 25                rmq[dp[b - (1 << k) + 1][k]] ? dp[a][k] : dp[b - (1 << k) + 1][k];
 26     }
 27 };
 28 //边的结构体定义
 29 struct Edge {
 30     int to, next;
 31 };
 32 
 33 Edge edge[MAXN * 2];
 34 
 35 int tot, head[MAXN];
 36 int F[MAXN * 2]; //欧拉序列，就是dfs遍历的顺序，长度为2*n-1,下标从1开始
 37 int P[MAXN];//P[i]表示点i在F中第一次出现的位置
 38 int cnt;
 39 ST st;
 40 map<string, int> Hash_zh;
 41 map<int, string> Hash_fa;
 42 
 43 void init() {
 44     tot = 0;
 45     memset(head, -1, sizeof(head));
 46     Hash_zh.clear();
 47     Hash_fa.clear();
 48 }
 49 
 50 void addedge(int u, int v) { //加边，无向边需要加两次
 51     edge[tot].to = v;
 52     edge[tot].next = head[u];
 53     head[u] = tot++;
 54 }
 55 
 56 void dfs(int u, int pre, int dep) {
 57     F[++cnt] = u;
 58     rmq[cnt] = dep;
 59     P[u] = cnt;
 60     for(int i = head[u]; i != -1; i = edge[i].next) {
 61         int v = edge[i].to;
 62         if(v == pre)continue;
 63         dfs(v, u, dep + 1);
 64         F[++cnt] = u;
 65         rmq[cnt] = dep;
 66     }
 67 }
 68 void LCA_init(int root, int node_num) { //查询LCA前的初始化
 69     cnt = 0;
 70     dfs(root, root, 0);
 71     st.init(2 * node_num - 1);
 72 }
 73 
 74 int query_lca(int u, int v) { //查询u,v的lca编号
 75     return F[st.query(P[u], P[v])];
 76 }
 77 
 78 bool flag[MAXN];
 79 
 80 int main() {
 81     int T, N;
 82     int u, v, cnt;
 83     string str_u, str_v;
 84     while(~scanf("%d", &N)) {
 85         init();
 86         cnt = 1;
 87         memset(flag, false, sizeof(flag));
 88         for(int i = 1; i <= N; i++) {
 89             //scanf("%d%d", &u, &v);
 90             cin >> str_u >> str_v;
 91             if (Hash_zh[str_u] == 0) {
 92                 Hash_fa[cnt] = str_u;
 93                 Hash_zh[str_u] = cnt ++;
 94             }
 95             if (Hash_zh[str_v] == 0) {
 96                 Hash_fa[cnt] = str_v;
 97                 Hash_zh[str_v] = cnt ++;
 98             }
 99             u = Hash_zh[str_u];
100             v = Hash_zh[str_v];
101             addedge(u, v);
102             addedge(v, u);
103             flag[v] = true;
104         }
105         int root;
106         for(int i = 1; i <= N; i++) {
107             if(!flag[i]) {
108                 root = i;
109                 break;
110             }
111         }
112         LCA_init(root, N);
113         int query_n;
114         scanf ("%d", &query_n);
115         for (int i = 1; i <= query_n; ++ i) {
116             //scanf("%d%d", &u, &v);
117             cin >> str_u >> str_v;
118 
119             if (str_u == str_v) {
120                 cout << str_u << endl;
121                 continue;
122             }
123 
124             u = Hash_zh[str_u];
125             v = Hash_zh[str_v];
126             cout << Hash_fa[query_lca(u, v)] << endl;
127         }
128     }
129     return 0;
130 }