ACM学习历程—HDU5423 Rikka with Tree(搜索)
For a tree T, let F(T,i) be the distance between vertice 1 and vertice i.(The length of each edge is 1).
Two trees A and B are similiar if and only if the have same number of vertices and for each i meet F(A,i)=F(B,i).
Two trees A and B are different if and only if they have different numbers of vertices or there exist an number i which vertice i have different fathers in tree A and tree B when vertice 1 is root.
Tree A is special if and only if there doesn't exist an tree B which A and B are different and A and B are similiar.
Now he wants to know if a tree is special.
It is too difficult for Rikka. Can you help her?
For each testcase, the first line contains a number n(1≤n≤1000).
Then n−1 lines follow. Each line contains two numbers u,v(1≤u,v≤n) , which means there is an edge between u and v.
For the second testcase, this tree is similiar with the given tree:
题目要求的那个特殊的树其实就是一条直链,然后在链的末端接上若干节点,类似于扫帚的形状。
也就是最后一层的节点下方没有子节点,倒数第二层的节点下方可以有若干子节点,其余节点均只有一个子节点。
用dfs搜索每一层的节点进行判断即可。
代码:
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <set>
#include <queue>
#include <vector>
#define LL long long using namespace std; const int maxN = ; struct Edge
{
int to, next;
//int val;
}edge[maxN*]; int head[maxN], cnt; void addEdge(int u, int v)
{
edge[cnt].to = v;
edge[cnt].next = head[u];
head[u] = cnt;
cnt++;
} void initEdge()
{
memset(head, -, sizeof(head));
cnt = ;
} int n;
bool vis[maxN];
int maxDepth;
bool flag; bool input()
{
if (scanf("%d", &n) == EOF)
return false;
initEdge();
memset(vis, false, sizeof(vis));
maxDepth = ;
flag = true;
int u, v;
for (int i = ; i < n; ++i)
{
scanf("%d%d", &u, &v);
addEdge(u, v);
addEdge(v, u);
}
return true;
} void dfs(int now, int depth)
{
if (flag == false)
return;
int cnt = ;
vis[now] = true;
for (int i = head[now]; i != -; i = edge[i].next)
{
if (vis[edge[i].to])
continue;
dfs(edge[i].to, depth+);
cnt++;
}
if (cnt == )
return;
maxDepth = max(maxDepth, depth);
if (depth != maxDepth && cnt != )
flag = false;
} void work()
{
dfs(, );
if (flag)
printf("YES\n");
else
printf("NO\n");
} int main()
{
//freopen("test.in", "r", stdin);
while (input())
{
work();
}
return ;
}
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