[백준] 17420번 : 깊콘이 넘쳐흘러

https://www.acmicpc.net/problem/17420

use io::Write;
use std::{io, str};

pub struct UnsafeScanner<R> {
  reader: R,
  buf_str: Vec<u8>,
  buf_iter: str::SplitAsciiWhitespace<'static>,
}

impl<R: io::BufRead> UnsafeScanner<R> {
  pub fn new(reader: R) -> Self {
    Self {
      reader,
      buf_str: vec![],
      buf_iter: "".split_ascii_whitespace(),
    }
  }

  pub fn token<T: str::FromStr>(&mut self) -> T {
    loop {
      if let Some(token) = self.buf_iter.next() {
        return token.parse().ok().expect("Failed parse");
      }
      self.buf_str.clear();
      self.reader
          .read_until(b'\n', &mut self.buf_str)
          .expect("Failed read");
      self.buf_iter = unsafe {
        let slice = str::from_utf8_unchecked(&self.buf_str);
        std::mem::transmute(slice.split_ascii_whitespace())
      }
    }
  }

  pub fn token_eof<T: str::FromStr>(&mut self) -> Option<T> {
    loop {
      if let Some(token) = self.buf_iter.next() {
        return token.parse().ok();
      }
      self.buf_str.clear();
      if self.reader.read_until(b'\n', &mut self.buf_str).unwrap() == 0 {
        return None;
      }
      self.buf_iter = unsafe {
        let slice = str::from_utf8_unchecked(&self.buf_str);
        std::mem::transmute(slice.split_ascii_whitespace())
      }
    }
  }
}

fn main() {
  let (stdin, stdout) = (io::stdin(), io::stdout());
  let mut scan = UnsafeScanner::new(stdin.lock());
  let mut out = io::BufWriter::new(stdout.lock());

  let n = scan.token::<usize>();
  let (a, b) = ((0..n).map(|_| scan.token::<i64>()).collect::<Vec<_>>(), (0..n).map(|_| scan.token::<i64>()).collect::<Vec<_>>());

  let mut arr = (0..n).map(|idx| (a[idx], b[idx])).collect::<Vec<_>>();

  arr.sort_unstable_by(|a, b| a.1.cmp(&b.1).then(a.0.cmp(&b.0)));

  let mut answer = 0;
  let (mut prev_max, mut day_max) = (arr[0].1, -1);

  for i in 0..n {
    if prev_max > arr[i].0 {
      if prev_max < arr[i].1 {
        prev_max = arr[i].1;
      }

      let count = ((prev_max - arr[i].0) + 29) / 30;
      arr[i].0 += count * 30;

      answer += count;
    }

    day_max = day_max.max(arr[i].0);

    if i + 1 < n && arr[i].1 != arr[i + 1].1 {
      prev_max = day_max;
    }
  }
  write!(out, "{}", answer).unwrap();
}