PAT甲级练习题A1004. Counting Leaves

题目描述

A family hierarchy is usually presented by a pedigree tree. Your job is to count those family members who have no child.
Input

Each input file contains one test case. Each case starts with a line containing 0 < N < 100, the number of nodes in a tree, and M (< N), the number of non-leaf nodes. Then M lines follow, each in the format:

ID K ID[1] ID[2] … ID[K]
where ID is a two-digit number representing a given non-leaf node, K is the number of its children, followed by a sequence of two-digit ID’s of its children. For the sake of simplicity, let us fix the root ID to be 01.
Output

For each test case, you are supposed to count those family members who have no child for every seniority level starting from the root. The numbers must be printed in a line, separated by a space, and there must be no extra space at the end of each line.

The sample case represents a tree with only 2 nodes, where 01 is the root and 02 is its only child. Hence on the root 01 level, there is 0 leaf node; and on the next level, there is 1 leaf node. Then we should output “0 1” in a line.

Sample Input
2 1
01 1 02
Sample Output
0 1

题目解析

就是建立一个树，找到每一个深度的叶子数（即没有子叶的节点数），使用宽度遍历法（BFS），很方便就找出来了，注意输出的时候是按照层次输出，所以要为每个节点标记深度值（即代数）。

代码

#include
#include
#include
using namespace std;

int main()
{

  int N, M, ID, K, kid;
  cin >> N >> M;
  vector<vector<int> >nodes(N+1);
  for (int i = 0; i < M; ++i)
  {
    cin >> ID >> K;
    for (int j = 0; j < K; ++j)
    {
      cin >> kid;
      nodes[ID].push_back(kid);
    }
  }
  int cnt = 0, gen = 0;
  vector<int>generation(N+1,0);
  deque<int> L;
  L.push_back(1);
  while (!L.empty())
  {
    int id = L.front();
    L.pop_front();
    if (generation[id] > gen)
    {
      if (gen == 0)
      {
        cout << cnt;
      }
      else
      {
        cout << " " << cnt;
      }
      ++gen;
      cnt = 0;
    }

    if (!nodes[id].empty())
    {
      for (int i = 0; i < nodes[id].size(); ++i)
      {
        L.push_back(nodes[id][i]);
        generation[nodes[id][i]] = generation[id] + 1;
      }
    }
    else
    {
      ++cnt;
    }

  }
  if (gen == 0)
  {
    cout << cnt;
  }
  else
  {
    cout << " " << cnt;
  }
  system("pause");
  return 0;
}