ABC167

https://atcoder.jp/contests/abc167
過去問。
　

A: Registration

s = gets.chomp
t = gets.chomp

puts (t[0..-2] == s) ? "Yes" : "No" 

B: Easy Linear Programming

a, b, c, k = gets.split.map(&:to_i)

score = 0

if a <= k
  score += a
  k -= a
  if b <= k
    k -= b
    if c <= k
      score -= c
    else
      score -= k
    end
  end
else
  score += k
end

puts score

C: Skill Up

全探索なのだけれど、ちょっと自信がなかった。一発で通ってホッ。

n, m, x = gets.split.map(&:to_i)
books = n.times.map {gets.split.map(&:to_i)}

min = 1200001

(1..n).each do |i|
  books.combination(i) do |selected|
    cost = 0
    f = selected.map {|price, *up|
      cost += price
      up
    }.transpose.map(&:sum).all? {_1 >= x}
    if f
      min = cost if cost < min
    end
  end
end

puts (min == 1200001) ? -1 : min

D: Teleporter

これは考えた。エッジケースがむずかしかった。

n, k = gets.split.map(&:to_i)
destinations = gets.split.map(&:to_i)

teleport = [1]
visited = Array.new(200001)
visited[1] = true

now = 1
while true
  nxt = destinations[now - 1]
  teleport << nxt
  break if visited[nxt]
  visited[nxt] = true
  now = nxt
end

idx = teleport.index(nxt)
ts = teleport.size
ans = if k < ts
        teleport[k]
      else
        loop_size = ts - idx - 1
        teleport[(k - idx) % loop_size + idx]
      end

puts ans