ZOJ --- 3516 Tree of Three

Tree of Three

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Time Limit: 2 Seconds      Memory Limit: 65536 KB

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Now we have a tree and some queries to deal with. Every node in the tree has a value on it. For one node A, we want to know the largest three values in all the nodes of the subtree whose root is node A. Node 0 is root of the tree, except it, all other nodes have a parent node.

Input

There are several test cases. Each test case begins with a line contains one integer n(1 ≤ n ≤ 10000), which indicates the number of the node in the tree. The second line contains one integer v[0], the value on the root. Then for the following n - 1 lines(from the 3rd line to the (n + 1)th line), let i + 2 be the line number, then line i + 2contains two integers parent and v[i], here parent is node i's parent node, v[i] is the value on node i. Here 0 ≤ v[i] ≤ 1000000. Then the next line contains an integer m(1 ≤m ≤ 10000), which indicates the number of queries. Following m lines, each line contains one integer q, 0 ≤ q < n, it meas a query on node q.

Output

For each test case, output m lines, each line contains one or three integers. If the query asked for a node that has less than three nodes in the subtree, output a "-1"; otherwise, output the largest three values in the subtree, from larger to smaller.

Sample Input

5
1
0 10
0 5
2 7
2 8
5
0
1
2
3
4

Sample Output

10 8 7
-1
8 7 5
-1
-1

思路：深度优先搜索，一层一层由子节点向跟节点回溯。

1.

 #include<iostream>
 #include<algorithm>
 #include<cstring>
 #include<cstdio>
 #define MAX 11111
 using namespace std;
 int Three_Max[MAX][], val[MAX], cnt[MAX];
 typedef struct{
     int to, next;
 }Node;
 Node edge[MAX];
 int head[MAX];
 void AddEdge(int u, int v, int i){
     edge[i].to = v;
     edge[i].next = head[u];
     head[u] = i;
 }
 bool cmp(int a, int b){
     return a > b;
 }
 void dfs(int id){
     cnt[id] = ;
     Three_Max[id][] = val[id];
     for(int i = head[id];i != -;i = edge[i].next){
         int u = edge[i].to;
         dfs(u);
         for(int j = ;j <= ;j ++) Three_Max[id][j] = Three_Max[u][j-];
         sort(Three_Max[id] + , Three_Max[id]+, cmp);
         cnt[id] += cnt[u];
     }
 }
 int main(){
     int n, m, cc, u, v, k;
     while(~scanf("%d", &n)){
         memset(head, -, sizeof(head));
         memset(Three_Max, , sizeof(Three_Max));
         memset(cnt, , sizeof(cnt));
         k = ;
         for(int i = ;i < n;i ++){
             if( == i){
                 scanf("%d", &cc);
                 val[] = cc;
             }else{
                 scanf("%d%d", &u, &cc);
                 val[i] = cc;
                 AddEdge(u, i, k);
                 k ++;
             }
         }
         dfs();
         scanf("%d", &m);
         for(int i = ;i < m;i ++){
             scanf("%d", &u);
             if(cnt[u] < ) printf("-1\n");
             else{
                 for(int j = ;j < ;j ++) printf("%d ", Three_Max[u][j]);
                 printf("%d\n", Three_Max[u][]);
             }
         }
     }
     return ;
 }

2.

 #include<iostream>
 #include<climits>
 #include<algorithm>
 #include<cstring>
 #include<cstdio>
 #define MAX 11111
 using namespace std;
 int Three_Max[MAX][], val[MAX], cnt[MAX];
 typedef struct{
     int to, next;
 }Node;
 Node edge[MAX];
 int head[MAX];
 void AddEdge(int u, int v, int i){
     edge[i].to = v;
     edge[i].next = head[u];
     head[u] = i;
 }
 bool cmp(int a, int b){
     return a > b;
 }
 int *dfs(int id){
     cnt[id] = ;
     Three_Max[id][] = val[id];
     for(int i = head[id];i != -;i = edge[i].next){
         int u = edge[i].to;
         int *temp = dfs(u);
         for(int j = ;j <= ;j ++) Three_Max[id][j] = temp[j-];
         sort(Three_Max[id] + , Three_Max[id]+, cmp);
         cnt[id] += cnt[u];
     }
     return Three_Max[id];
 }
 int main(){
     int n, m, cc, u, v, k;
     while(~scanf("%d", &n)){
         memset(head, -, sizeof(head));
         memset(Three_Max, , sizeof(Three_Max));
         memset(cnt, , sizeof(cnt));
         k = ;
         for(int i = ;i < n;i ++){
             if( == i){
                 scanf("%d", &cc);
                 val[] = cc;
             }else{
                 scanf("%d%d", &u, &cc);
                 val[i] = cc;
                 AddEdge(u, i, k);
                 k ++;
             }
         }
         dfs();
         scanf("%d", &m);
         for(int i = ;i < m;i ++){
             scanf("%d", &u);
             if(cnt[u] < ) printf("-1\n");
             else{
                 for(int j = ;j < ;j ++) printf("%d ", Three_Max[u][j]);
                 printf("%d\n", Three_Max[u][]);
             }
         }
     }
     return ;
 }