AtCoder Grand Contest 014
C
Closed Rooms
AtCoder
⌀ 1863
原题
← BD →
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Problem Statement

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Takahashi is locked within a building.

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This building consists of $H×W$ rooms, arranged in $H$ rows and $W$ columns. We will denote the room at the $i$-th row and $j$-th column as $(i,j)$. The state of this room is represented by a character $A_{i,j}$. If $A_{i,j}=$ #, the room is locked and cannot be entered; if $A_{i,j}=$ ., the room is not locked and can be freely entered. Takahashi is currently at the room where $A_{i,j}=$ S, which can also be freely entered.

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Each room in the $1$-st row, $1$-st column, $H$-th row or $W$-th column, has an exit. Each of the other rooms $(i,j)$ is connected to four rooms: $(i-1,j)$, $(i+1,j)$, $(i,j-1)$ and $(i,j+1)$.

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Takahashi will use his magic to get out of the building. In one cast, he can do the following:

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  • Move to an adjacent room at most $K$ times, possibly zero. Here, locked rooms cannot be entered.
  • Then, select and unlock at most $K$ locked rooms, possibly zero. Those rooms will remain unlocked from then on.
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His objective is to reach a room with an exit. Find the minimum necessary number of casts to do so.

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It is guaranteed that Takahashi is initially at a room without an exit.

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Constraints

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  • $3 ≤ H ≤ 800$
  • $3 ≤ W ≤ 800$
  • $1 ≤ K ≤ H×W$
  • Each $A_{i,j}$ is # , . or S.
  • There uniquely exists $(i,j)$ such that $A_{i,j}=$ S, and it satisfies $2 ≤ i ≤ H-1$ and $2 ≤ j ≤ W-1$.
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Input

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Input is given from Standard Input in the following format:

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H W K
A_{1,1}A_{1,2}...A_{1,W}
:
A_{H,1}A_{H,2}...A_{H,W}

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Output

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Print the minimum necessary number of casts.

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样例

Input #1
3 3 3
#.#
#S.
###
Output #1
1
Takahashi can move to room $(1,2)$ in one cast.
Input #2
3 3 3
###
#S#
###
Output #2
2
Takahashi cannot move in the first cast, but can unlock room $(1,2)$. Then, he can move to room $(1,2)$ in the next cast, achieving the objective in two casts.
Input #3
7 7 2
#######
#######
##...##
###S###
##.#.##
###.###
#######
Output #3
2
题目信息
题号
agc014_c
时间限制
2 s
内存限制
256 MB

题面与样例版权归 AtCoder 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。