PAT_A1110#Complete Binary Tree

Source:

PAT A1110 Complete Binary Tree (25 分)

Description:

Given a tree, you are supposed to tell if it is a complete binary tree.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤) which is the total number of nodes in the tree -- and hence the nodes are numbered from 0 to N−1. Then N lines follow, each corresponds to a node, and gives the indices of the left and right children of the node. If the child does not exist, a - will be put at the position. Any pair of children are separated by a space.

Output Specification:

For each case, print in one line YES and the index of the last node if the tree is a complete binary tree, or NO and the index of the root if not. There must be exactly one space separating the word and the number.

Sample Input 1:

9
7 8
- -
- -
- -
0 1
2 3
4 5
- -
- -

Sample Output 1:

YES 8

Sample Input 2:

8
- -
4 5
0 6
- -
2 3
- 7
- -
- -

Sample Output 2:

NO 1

Keys:

• 完全二叉树（Complete Binary Tree）

Attention:

• atoi(s.c_str()); 字符串转化为int，atof 对应 double，atoll 对应 long long；
• 含非数字则截取前面的数字部分，首字符非数字则返回0

Code:

 #include<cstdio>
 #include<string>
 #include<queue>
 #include<iostream>
 using namespace std;
 const int M=;
 int h[M]={};
 struct node
 {
     int left,right;
 }tree[M];

 bool isComplete(int root, int &last)
 {
     queue<int> q;
     q.push(root);
     while(!q.empty())
     {
         root = q.front();
         q.pop();
         if(root != -)
         {
             last = root;
             q.push(tree[root].left);
             q.push(tree[root].right);
         }
         else
         {
             while(!q.empty())
             {
                 if(q.front() != -)
                     return false;
                 q.pop();
             }
         }
     }
     return true;
 }

 int main()
 {
 #ifdef    ONLINE_JUDGE
 #else
     freopen("Test.txt", "r", stdin);
 #endif

     int n,root,last;
     scanf("%d", &n);
     for(int i=; i<n; i++)
     {
         string l,r;
         cin >> l >> r;
         if(l == "-")
             tree[i].left=-;
         else{
             tree[i].left = atoi(l.c_str());
             h[tree[i].left]=;
         }
         if(r == "-")
             tree[i].right=-;
         else{
             tree[i].right = atoi(r.c_str());
             h[tree[i].right]=;
         }
     }
     for(int i=; i<n; i++){
         if(h[i]==){
             root=i;
             break;
         }
     }
     if(isComplete(root, last))
         printf("YES %d", last);
     else
         printf("NO %d", root);

     return ;
 }