atcoder#ABC276E. [ABC276E] Round Trip

[ABC276E] Round Trip

Score : 500500 points

Problem Statement

We have a grid with HH rows from top to bottom and WW columns from left to right. Let (i,j)(i, j) denote the ii-th row from the top (1iH)(1 \leq i \leq H) and jj-th column from the left (1jW)(1 \leq j \leq W).

Each square is one of the following: the initial point, a road, and an obstacle. A square (i,j)(i, j) is represented by a character Ci,jC_{i, j}. The square is the initial point if Ci,j=C_{i, j} = S, a road if Ci,j=C_{i, j} = ., and an obstacle if Ci,j=C_{i, j} = #. There is exactly one initial point.

Determine whether there is a path of length 44 or greater that starts at the initial point, repeats moving vertically or horizontally to an adjacent square, and returns to the initial point without going through an obstacle or visiting the same square multiple times except at the beginning and the end. More formally, determine whether there are an integer nn and a sequence of squares (x0,y0),(x1,y1),,(xn,yn)(x_0, y_0), (x_1, y_1), \dots, (x_n, y_n) that satisfy the following conditions.

  • n4n \geq 4.
  • Cx0,y0=Cxn,yn=C_{x_0, y_0} = C_{x_n, y_n} = S.
  • If 1in11 \leq i \leq n - 1, then Cxi,yi=C_{x_i, y_i} = ..
  • If 1i<jn11 \leq i \lt j \leq n - 1, then (xi,yi)(xj,yj)(x_i, y_i) \neq (x_j, y_j).
  • If 0in10 \leq i \leq n - 1, then square (xi,yi)(x_i, y_i) and square (xi+1,yi+1)(x_{i+1}, y_{i+1}) are vertically or horizontally adjacent to each other.

Constraints

  • 4H×W1064 \leq H \times W \leq 10^6
  • HH and WW are integers greater than or equal to 22.
  • Ci,jC_{i, j} is S, ., or #.
  • There is exactly one (i,j)(i, j) such that Ci,j=C_{i, j} = S.

Input

The input is given from Standard Input in the following format:

HH WW

C1,1C1,WC_{1, 1} \ldots C_{1, W}

\vdots

CH,1CH,WC_{H, 1} \ldots C_{H, W}

Output

If there is a path that satisfies the conditions in the Problem Statement, print Yes; otherwise, print No.

4 4
....
#.#.
.S..
.##.
Yes

The path $(3, 2) \rightarrow (2, 2) \rightarrow (1, 2) \rightarrow (1, 3) \rightarrow (1, 4) \rightarrow (2, 4) \rightarrow (3, 4) \rightarrow (3, 3) \rightarrow (3, 2)$ satisfies the conditions.

2 2
S.
.#
No
5 7
.#...#.
..#.#..
...S...
..#.#..
.#...#.
No