Codeforces Round 425 (Div. 2)
D
Misha, Grisha and Underground
Codeforces
1900
原题
← CE →
翻译中…

Misha and Grisha are funny boys, so they like to use new underground. The underground has $*n*$ stations connected with $*n* - 1$ routes so that each route connects two stations, and it is possible to reach every station from any other.

翻译中…

The boys decided to have fun and came up with a plan. Namely, in some day in the morning Misha will ride the underground from station $*s*$ to station $*f*$ by the shortest path, and will draw with aerosol an ugly text "Misha was here" on every station he will pass through (including $*s*$ and $*f*$). After that on the same day at evening Grisha will ride from station $*t*$ to station $*f*$ by the shortest path and will count stations with Misha's text. After that at night the underground workers will wash the texts out, because the underground should be clean.

翻译中…

The boys have already chosen three stations $*a*$, $*b*$ and $*c*$ for each of several following days, one of them should be station $*s*$ on that day, another should be station $*f*$, and the remaining should be station $*t*$. They became interested how they should choose these stations $*s*$, $*f*$, $*t*$ so that the number Grisha will count is as large as possible. They asked you for help.

翻译中…

Input

翻译中…

The first line contains two integers $*n*$ and $*q*$ ($2 ≤ *n* ≤ 10^{5}$, $1 ≤ *q* ≤ 10^{5}$) — the number of stations and the number of days.

翻译中…

The second line contains $*n* - 1$ integers $*p*_{2}, *p*_{3}, ..., *p*_{*n*}$ ($1 ≤ *p*_{*i*} ≤ *n*$). The integer $*p*_{*i*}$ means that there is a route between stations $*p*_{*i*}$ and $*i*$. It is guaranteed that it's possible to reach every station from any other.

翻译中…

The next $*q*$ lines contains three integers $*a*$, $*b*$ and $*c*$ each ($1 ≤ *a*, *b*, *c* ≤ *n*$) — the ids of stations chosen by boys for some day. Note that some of these ids could be same.

翻译中…

Output

翻译中…

Print $*q*$ lines. In the $*i*$-th of these lines print the maximum possible number Grisha can get counting when the stations $*s*$, $*t*$ and $*f*$ are chosen optimally from the three stations on the $*i*$-th day.

翻译中…

Note

翻译中…

In the first example on the first day if $*s*$ = $1$, $*f*$ = $2$, $*t*$ = $3$, Misha would go on the route $1$ image $2$, and Grisha would go on the route $3$ image $1$ image $2$. He would see the text at the stations $1$ and $2$. On the second day, if $*s*$ = $3$, $*f*$ = $2$, $*t*$ = $3$, both boys would go on the route $3$ image $1$ image $2$. Grisha would see the text at $3$ stations.

翻译中…

In the second examle if $*s*$ = $1$, $*f*$ = $3$, $*t*$ = $2$, Misha would go on the route $1$ image $2$ image $3$, and Grisha would go on the route $2$ image $3$ and would see the text at both stations.

翻译中…

样例

Input #1
3 2
1 1
1 2 3
2 3 3
Output #1
2
3
InputCopy OutputCopy
Input #2
4 1
1 2 3
1 2 3
Output #2
2
InputCopy OutputCopy
题目信息
题号
832D
时间限制
2 s
内存限制
256 MB
标签
DFS 及类似
图论
树

题面与样例版权归 Codeforces 及出题人所有;中文翻译由 AI 生成(CI 管线),如有出入请以原文为准。