hihoCoder#1069 最近公共祖先·三

原题地址

根据提示用Spase Table做

将Tree先展成List，因为数组长度等于边数的2倍，树中边数等于节点数-1，所以List数组只要开2倍节点数大小即可

WA了几次，原来是查询的时候出现左边界大于右边界的情况，所以这种情况要颠倒一下

代码：

 #include <iostream>
 #include <vector>
 #include <string>
 #include <map>

 using namespace std;

 #define MAX_NODE 100005

 int N, M;
 map<string, int> a2i;
 string i2a[MAX_NODE];
 int traverse_path[MAX_NODE * ];
 int depth[MAX_NODE];
 int st[MAX_NODE * ][]; // 保存的是节点编号
 vector<int> child[MAX_NODE];
 int last_position[MAX_NODE];
 int path_length = ;
 int tree_size = ;

 void traverse(int r, int d) {
   traverse_path[path_length++] = r;
   depth[r] = d;
   for (auto c : child[r]) {
     traverse(c, d + );
     traverse_path[path_length++] = r;
   }
   last_position[r] = path_length - ;
 }

 void build() {
   for (int i = ; i < path_length; i++)
     st[i][] = traverse_path[i];

   for (int j = ; ( << j) <= path_length; j++) {
     for (int i = ; i + ( << j) <= path_length; i++) {
       int a = st[i][j - ];
       int b = st[i + ( << (j - ))][j - ];
       st[i][j] = depth[a] < depth[b] ? a : b;
     }
   }
 }

 int query(int l, int r) {
   if (l > r)
     return query(r, l);
   int len = r - l + ;
   int i = ;
   while (( << (i + )) <= len)
     i++;
   int a = st[l][i];
   int b = st[r - ( << i) + ][i];
   return depth[a] < depth[b] ? a : b;
 }

 int main() {
   scanf("%d", &N);
   for (int i = ; i < N; i++) {
     string a, b;
     int ai, bi;
     cin >> a >> b;
     if (a2i.find(a) == a2i.end()) {
       ai = a2i[a] = tree_size;
       i2a[ai] = a;
       tree_size++;
     }
     else
       ai = a2i[a];
     if (a2i.find(b) == a2i.end()) {
       bi = a2i[b] = tree_size;
       i2a[bi] = b;
       tree_size++;
     }
     else
       bi = a2i[b];
     child[ai].push_back(bi);
   }

   traverse(, );
   build();

   scanf("%d", &M);
   while (M--) {
     string a, b;
     int ai, bi;
     cin >> a >> b;
     ai = a2i[a];
     bi = a2i[b];
     cout << i2a[query(last_position[ai], last_position[bi])] << endl;
   }

   return ;
 }