use std::cmp::*; use std::collections::*; // https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 macro_rules! input { ($($r:tt)*) => { let stdin = std::io::stdin(); let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock())); let mut next = move || -> String{ bytes.by_ref().map(|r|r.unwrap() as char) .skip_while(|c|c.is_whitespace()) .take_while(|c|!c.is_whitespace()) .collect() }; input_inner!{next, $($r)*} }; } macro_rules! input_inner { ($next:expr) => {}; ($next:expr,) => {}; ($next:expr, $var:ident : $t:tt $($r:tt)*) => { let $var = read_value!($next, $t); input_inner!{$next $($r)*} }; } macro_rules! read_value { ($next:expr, [ $t:tt ; $len:expr ]) => { (0..$len).map(|_| read_value!($next, $t)).collect::>() }; ($next:expr, chars) => { read_value!($next, String).chars().collect::>() }; ($next:expr, $t:ty) => ($next().parse::<$t>().expect("Parse error")); } // Solved with hints fn main() { input! { h: usize, w: usize, s: [chars; h], } let mut s = s; for i in 0..h { s[i].insert(0, '#'); s[i].push('#'); } s.insert(0, vec!['#'; w + 1]); s.push(vec!['#'; w + 1]); const INF: i32 = 1 << 28; let mut que = BinaryHeap::new(); let mut dist = vec![vec![INF; w + 2]; h + 2]; for i in 4..w + 2 { que.push((Reverse(0), 0, i)); } for i in 0..h - 2 { que.push((Reverse(0), i, w + 1)); } while let Some((Reverse(d), x, y)) = que.pop() { if dist[x][y] <= d { continue; } dist[x][y] = d; for dx in -3i32..=3 { for dy in -3i32..=3 { if dx.abs() == 3 && dy.abs() == 3 { continue; } let nx = (x as i32 + dx) as usize; let ny = (y as i32 + dy) as usize; if nx >= h || ny >= w { continue; } if nx <= 3 && ny <= 3 { continue; } if nx >= h - 2 && ny >= w - 2 { continue; } que.push((Reverse(d + if s[nx][ny] == '#' { 0 } else { 1 }), nx, ny)); } } } let mut ans = INF; for i in 4..h + 2 { ans = min(ans, dist[i][0]); } for i in 0..w - 2 { ans = min(ans, dist[h + 1][i]); } println!("{}", ans); }