백준 온라인 저지, DFS / 13565번: 침투 (파이썬 / , 백준 실버문제)

문제

인제대학교 생화학연구실에 재직중인 석교수는 전류가 침투(percolate) 할 수 있는 섬유 물질을 개발하고 있다. 이 섬유 물질은 2차원 M × N 격자로 표현될 수 있다. 편의상 2차원 격자의 위쪽을 바깥쪽(outer side), 아래쪽을 안쪽(inner side)라고 생각하기로 한다. 또한 각 격자는 검은색 아니면 흰색인데, 검은색은 전류를 차단하는 물질임을 뜻하고 흰색은 전류가 통할 수 있는 물질임을 뜻한다. 전류는 섬유 물질의 가장 바깥쪽 흰색 격자들에 공급되고, 이후에는 상하좌우로 인접한 흰색 격자들로 전달될 수 있다.

김 교수가 개발한 섬유 물질을 나타내는 정보가 2차원 격자 형태로 주어질 때, 바깥쪽에서 흘려 준 전류가 안쪽까지 침투될 수 있는지 아닌지를 판단하는 프로그램을 작성하시오.

(a) The current percolates.	(b) The current does not percolate.

예를 들어, Figure 1(a) 에서는 바깥쪽에서 공급된 전류가 안쪽까지 침투하지만, Figure 1(b)에서는 그렇지 못한다.

입력

첫째 줄에는 격자의 크기를 나타내는  M (2 ≤ M ≤ 1,000) 과 N (2 ≤ N ≤ 1,000) 이 주어진다. M줄에 걸쳐서, N개의 0 또는 1 이 공백 없이 주어진다. 0은 전류가 잘 통하는 흰색, 1은 전류가 통하지 않는 검은색 격자임을 뜻한다.

출력

바깥에서 흘려준 전류가 안쪽까지 잘 전달되면 YES를 출력한다.

그렇지 않으면 NO를 출력한다.

제한

예제 입력 1

5 6
010101
010000
011101
100011
001011

예제 출력 1

NO

예제 입력 2

8 8
11000111
01100000
00011001
11001000
10001001
10111100
01010000
00001011

예제 출력 2

YES

힌트

[{"problem_id":"13565","problem_lang":"0","title":"\uce68\ud22c","description":"<p>\uc778\uc81c\ub300\ud559\uad50 \uc0dd\ud654\ud559\uc5f0\uad6c\uc2e4\uc5d0 \uc7ac\uc9c1\uc911\uc778&nbsp;\uc11d\uad50\uc218\ub294 \uc804\ub958\uac00 \uce68\ud22c(percolate) \ud560 \uc218 \uc788\ub294 \uc12c\uc720 \ubb3c\uc9c8\uc744 \uac1c\ubc1c\ud558\uace0 \uc788\ub2e4. \uc774 \uc12c\uc720 \ubb3c\uc9c8\uc740 2\ucc28\uc6d0 M&nbsp;&times; N \uaca9\uc790\ub85c \ud45c\ud604\ub420 \uc218 \uc788\ub2e4.&nbsp;\ud3b8\uc758\uc0c1 2\ucc28\uc6d0 \uaca9\uc790\uc758 \uc704\ucabd\uc744 \ubc14\uae65\ucabd(outer side), \uc544\ub798\ucabd\uc744 \uc548\ucabd(inner side)\ub77c\uace0 \uc0dd\uac01\ud558\uae30\ub85c \ud55c\ub2e4. \ub610\ud55c \uac01 \uaca9\uc790\ub294 \uac80\uc740\uc0c9 \uc544\ub2c8\uba74 \ud770\uc0c9\uc778\ub370, \uac80\uc740\uc0c9\uc740 \uc804\ub958\ub97c \ucc28\ub2e8\ud558\ub294 \ubb3c\uc9c8\uc784\uc744 \ub73b\ud558\uace0 \ud770\uc0c9\uc740 \uc804\ub958\uac00 \ud1b5\ud560 \uc218 \uc788\ub294 \ubb3c\uc9c8\uc784\uc744 \ub73b\ud55c\ub2e4. \uc804\ub958\ub294 \uc12c\uc720 \ubb3c\uc9c8\uc758 \uac00\uc7a5 \ubc14\uae65\ucabd \ud770\uc0c9 \uaca9\uc790\ub4e4\uc5d0 \uacf5\uae09\ub418\uace0, \uc774\ud6c4\uc5d0\ub294 \uc0c1\ud558\uc88c\uc6b0\ub85c \uc778\uc811\ud55c \ud770\uc0c9 \uaca9\uc790\ub4e4\ub85c \uc804\ub2ec\ub420 \uc218 \uc788\ub2e4.<\/p>\r\n\r\n<p>\uae40 \uad50\uc218\uac00 \uac1c\ubc1c\ud55c \uc12c\uc720 \ubb3c\uc9c8\uc744 \ub098\ud0c0\ub0b4\ub294&nbsp;\uc815\ubcf4\uac00 2\ucc28\uc6d0 \uaca9\uc790 \ud615\ud0dc\ub85c \uc8fc\uc5b4\uc9c8 \ub54c, \ubc14\uae65\ucabd\uc5d0\uc11c \ud758\ub824 \uc900 \uc804\ub958\uac00 \uc548\ucabd\uae4c\uc9c0 \uce68\ud22c\ub420 \uc218 \uc788\ub294\uc9c0 \uc544\ub2cc\uc9c0\ub97c \ud310\ub2e8\ud558\ub294 \ud504\ub85c\uadf8\ub7a8\uc744 \uc791\uc131\ud558\uc2dc\uc624.<\/p>\r\n\r\n<table class=\"table\" style=\"width:100%\">\r\n\t<tbody>\r\n\t\t<tr>\r\n\t\t\t<td style=\"text-align:center\"><img alt=\"\" src=\"https:\/\/onlinejudgeimages.s3-ap-northeast-1.amazonaws.com\/problem\/13565\/1.png\" style=\"height:163px; width:129px\" \/><\/td>\r\n\t\t\t<td style=\"text-align:center\"><img alt=\"\" src=\"https:\/\/onlinejudgeimages.s3-ap-northeast-1.amazonaws.com\/problem\/13565\/2.png\" style=\"height:157px; width:127px\" \/><\/td>\r\n\t\t<\/tr>\r\n\t\t<tr>\r\n\t\t\t<td style=\"text-align:center\">(a) The current percolates.<\/td>\r\n\t\t\t<td style=\"text-align:center\">(b) The current does not percolate.<\/td>\r\n\t\t<\/tr>\r\n\t<\/tbody>\r\n<\/table>\r\n\r\n<p>\uc608\ub97c \ub4e4\uc5b4, Figure 1(a) \uc5d0\uc11c\ub294 \ubc14\uae65\ucabd\uc5d0\uc11c \uacf5\uae09\ub41c \uc804\ub958\uac00&nbsp;\uc548\ucabd\uae4c\uc9c0 \uce68\ud22c\ud558\uc9c0\ub9cc, Figure 1(b)\uc5d0\uc11c\ub294 \uadf8\ub807\uc9c0 \ubabb\ud55c\ub2e4.<\/p>\r\n","input":"<p>\uccab\uc9f8 \uc904\uc5d0\ub294 \uaca9\uc790\uc758 \ud06c\uae30\ub97c \ub098\ud0c0\ub0b4\ub294 &nbsp;M (2 &le; M &le; 1,000)&nbsp;\uacfc N (2 &le; N &le; 1,000) \uc774 \uc8fc\uc5b4\uc9c4\ub2e4. M\uc904\uc5d0 \uac78\uccd0\uc11c, N\uac1c\uc758 0 \ub610\ub294 1 \uc774 \uacf5\ubc31 \uc5c6\uc774 \uc8fc\uc5b4\uc9c4\ub2e4. 0\uc740 \uc804\ub958\uac00 \uc798 \ud1b5\ud558\ub294 \ud770\uc0c9, 1\uc740&nbsp;\uc804\ub958\uac00 \ud1b5\ud558\uc9c0&nbsp;\uc54a\ub294&nbsp;\uac80\uc740\uc0c9 \uaca9\uc790\uc784\uc744 \ub73b\ud55c\ub2e4.<\/p>\r\n","output":"<p>\ubc14\uae65\uc5d0\uc11c \ud758\ub824\uc900 \uc804\ub958\uac00 \uc548\ucabd\uae4c\uc9c0 \uc798 \uc804\ub2ec\ub418\uba74 YES\ub97c \ucd9c\ub825\ud55c\ub2e4.<\/p>\r\n\r\n<p>\uadf8\ub807\uc9c0 \uc54a\uc73c\uba74 NO\ub97c \ucd9c\ub825\ud55c\ub2e4.<\/p>\r\n","hint":"","original":"0","html_title":"0","problem_lang_tcode":"Korean"},{"problem_id":"13565","problem_lang":"1","title":"Percolation","description":"<p>Professor Kim is in the process of developing a new fabric material such that the electrical current percolates. The cross section of the new fabric can be shown in the two-dimensional M &times; N grid. We assume that the top of the grid is the outer side of the fabric and the bottom is the inner side. The black colored cell insulates the current while the white cell conducts the current. The current travels from the outer side to the inner side of the fabric only through the white cells that are adjacent to each other. When the white cells are connected diagonally, the current cannot flow (see Figure 1). The professor wants to test whether the current could percolate from the outer side to the inner side through the material or not.<\/p>\r\n\r\n<p>For example, the following Figure 1(a) shows that the current percolates through the material but Figure 1(b) does not:<\/p>\r\n\r\n<table class=\"table\" style=\"width:100%\">\r\n\t<tbody>\r\n\t\t<tr>\r\n\t\t\t<td style=\"text-align: center;\"><img alt=\"\" src=\"https:\/\/onlinejudgeimages.s3-ap-northeast-1.amazonaws.com\/problem\/13565\/1.png\" style=\"height:163px; width:129px\" \/><\/td>\r\n\t\t\t<td style=\"text-align: center;\"><img alt=\"\" src=\"https:\/\/onlinejudgeimages.s3-ap-northeast-1.amazonaws.com\/problem\/13565\/2.png\" style=\"height:157px; width:127px\" \/><\/td>\r\n\t\t<\/tr>\r\n\t\t<tr>\r\n\t\t\t<td style=\"text-align: center;\">(a) The current percolates.<\/td>\r\n\t\t\t<td style=\"text-align: center;\">(b) The current does not percolate.<\/td>\r\n\t\t<\/tr>\r\n\t<\/tbody>\r\n<\/table>\r\n\r\n<p style=\"text-align: center;\">Figure 1. Two examples.<\/p>\r\n\r\n<p>When the information on each cell is given, write a program that computes whether the current can pass through the material or not.<\/p>\r\n","input":"<p>Your program is to read from standard input. The first line of the input contains two integers M (2 &le; M &le; 1,000) and N (2 &le; N &le; 1,000) which represent the size of the fabric. In the following M lines, the information about each cell is given. Each line consists of N characters which composed by &lsquo;0&rsquo; or &lsquo;1&rsquo;. The character &lsquo;0&rsquo; represents the conduct cell and &lsquo;1&rsquo; represents the insulate cell.<\/p>\r\n","output":"<p>Your program is to write to standard output. If the current can pass through the material from the top to the bottom, print YES. If not, print NO.<\/p>\r\n","hint":"","original":"1","html_title":"0","problem_lang_tcode":"English"}]

접근 방법

- DFS 탐색을 통해 첫번째 행에서 출발해 마지막 행에 도착하는지 판단한다.
- 만일 도착한다면 YES, 끝까지 도착하지 못한다면 NO를 출력한다.

코드

# https://www.acmicpc.net/problem/13565
# 접근 방법
# DFS 탐색을 통해 첫번째 행에서 출발해 마지막 행에 도착하는지 판단한다.
# 만일 도착한다면 YES, 끝까지 도착하지 못한다면 NO를 출력한다.
import sys
sys.setrecursionlimit(10**6)
def dfs(r, c):
    if r == m-1:
        return True
    for dr, dc in [[1, 0], [-1, 0], [0, 1], [0, -1]]:
        if 0<=r+dr