Exactly K Steps

AtCoder

IDabc267_f

Time2000ms

Memory256MB

Difficulty—

You are given a tree with $N$ vertices. The vertices are numbered $1, \dots, N$, and the $i$\-th ($1 \leq i \leq N - 1$) edge connects Vertices $A_i$ and $B_i$. We define the **distance** between Vertices $u$ and $v$ on this tree by the number of edges in the shortest path from Vertex $u$ to Vertex $v$. You are given $Q$ queries. In the $i$\-th ($1 \leq i \leq Q$) query, given integers $U_i$ and $K_i$, print the index of any vertex whose distance from Vertex $U_i$ is exactly $K_i$. If there is no such vertex, print `-1`. ## Constraints * $2 \leq N \leq 2 \times 10^5$ * $1 \leq A_i \lt B_i \leq N \, (1 \leq i \leq N - 1)$ * The given graph is a tree. * $1 \leq Q \leq 2 \times 10^5$ * $1 \leq U_i, K_i \leq N \, (1 \leq i \leq Q)$ * All values in input are integers. ## Input Input is given from Standard Input in the following format: $N$ $A_1$ $B_1$ $\vdots$ $A_{N-1}$ $B_{N-1}$ $Q$ $U_1$ $K_1$ $\vdots$ $U_Q$ $K_Q$ [samples]

Samples

Input #1

Output #1

4
1
-1

*   Two vertices, Vertices $4$ and $5$, have a distance exactly $2$ from Vertex $2$.
*   Only Vertex $1$ has a distance exactly $3$ from Vertex $5$.
*   No vertex has a distance exactly $3$ from Vertex $3$.

Input #2

Output #2

API Response (JSON)

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  "problem": {
    "name": "Exactly K Steps",
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      "content": "You are given a tree with $N$ vertices. The vertices are numbered $1, \\dots, N$, and the $i$\\-th ($1 \\leq i \\leq N - 1$) edge connects Vertices $A_i$ and $B_i$. We define the **distance** between Vert",
      "description_type": "Markdown"
    },
    "platform": "AtCoder",
    "limit": {
      "time_limit": 2000,
      "memory_limit": 262144
    },
    "difficulty": "None",
    "is_remote": true,
    "is_sync": true,
    "sync_url": null,
    "sign": "abc267_f"
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  "statements": [
    {
      "statement_type": "Markdown",
      "content": "You are given a tree with $N$ vertices. The vertices are numbered $1, \\dots, N$, and the $i$\\-th ($1 \\leq i \\leq N - 1$) edge connects Vertices $A_i$ and $B_i$.\nWe define the **distance** between Vert...",
      "is_translate": false,
      "language": "English"
    }
  ]
}

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