2024-07-19 01:57:26

Affected files: .obsidian/workspace.json src/content/blog/boj-2564-경비원.md
gyunseo · Jul 18, 2024 · 673a6dd · 673a6dd
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Showing 2 changed files with 141 additions and 12 deletions.
diff --git a/.obsidian/workspace.json b/.obsidian/workspace.json
@@ -4,16 +4,16 @@
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@@ -22,16 +22,16 @@
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diff --git a/src/content/blog/boj-2564-경비원.md b/src/content/blog/boj-2564-경비원.md
@@ -0,0 +1,129 @@
+---
+author: Gyunseo Lee
+title: "BOJ 백준 2564: 경비원"
+pubDatetime: 2024-07-19T01:53:00+09:00
+modDatetime: 2024-07-19T01:53:00+09:00
+featured: false
+draft: false
+tags:
+  - PS
+  - BOJ
+  - Algorithms
+  - 실랜디
+  - 골랜디
+  - BFS
+description: BFS 템플릿은 자다 깨도 5분만에 칠 수 있게 외우자
+ogImage: ""
+---
+
+## Table of contents
+
+## 들어가며
+
+걸린 시간: 27분
+
+문제를 읽고, 경우의 수를 나눠서 좌표 간의 거리를 계산하면 되지 않을까 싶었습니다.  
+그런데 웬걸 좌표의 범위, 타겟 좌표 개수의 범위 모두 100이하여서 이건 그냥 BFS로 돌리면 되겠다 싶어서, BFS로 돌렸습니다.
+
+## 접근
+
+![](https://res.cloudinary.com/gyunseo-blog/image/upload/f_auto/v1721321745/image_kdvjz5.png)
+저 박스에 해당하는 board를 생성해서 그 안에서 BFS를 돌리게 했습니다.  
+시간 복잡도는 O(상점 개수 \* 박스에 해당하는 보드의 크기) 최대값 넣고 계산해도 백만정도...
+
+## 구현
+
+```python
+import sys
+from collections import deque
+
+
+input = sys.stdin.readline
+
+def processPos(direction, pos):
+    ret_i, ret_j = -1, -1
+    # i = 0
+    if direction == 1:
+        ret_i, ret_j = (0, pos)
+    # i = height
+    elif direction == 2:
+        ret_i, ret_j = (height, pos)
+    # j = 0
+    elif direction == 3:
+        ret_i, ret_j = (pos, 0)
+    # j = width
+    elif direction == 4:
+        ret_i, ret_j = (pos, width)
+
+    return ret_i, ret_j
+
+def OOB(i, j):
+    if i < 0 or i > height:
+        return True
+    if j < 0 or j > width:
+        return True
+    return False
+
+def BFS(target_pos):
+    distance = [[0 for __ in range(width + 1)] for _ in range(height + 1)]
+    q = deque()
+    q.append(startPos)
+    distance[startPos[0]][startPos[1]] = 1
+
+    while q:
+        cur_i, cur_j = q.popleft()
+
+        for delta_i, delta_j in zip(deltaI, deltaJ):
+            next_i, next_j = cur_i + delta_i, cur_j + delta_j
+            if OOB(next_i, next_j):
+                continue
+            # 벽으로 막혀 있다면
+            if board[next_i][next_j] == 1:
+                continue
+            # 이미 방문한 곳이라면
+            if distance[next_i][next_j] > 0:
+                continue
+
+            distance[next_i][next_j] = distance[cur_i][cur_j] + 1
+            q.append((next_i, next_j))
+
+    return distance[target_pos[0]][target_pos[1]]
+
+if __name__ == "__main__":
+
+    width, height = map(int, input().strip().split())
+    numTargets = int(input().strip())
+    targetPosList = []
+    deltaI = (-1, 1, 0, 0)
+    deltaJ = (0, 0, -1, 1)
+    for _ in range(numTargets):
+        direction, pos = map(int, input().strip().split())
+
+        targetPosList.append(processPos(direction, pos))
+
+    direction, pos = map(int, input().strip().split())
+    startPos = processPos(direction, pos)
+
+    board = [[0 for __ in range(width + 1)] for _ in range(height + 1)]
+    ans = 0
+    # fill wall inner board
+    for i in range(height + 1):
+        for j in range(width + 1):
+            if i == 0 or i == height:
+                continue
+            if j == 0 or j == width:
+                continue
+            board[i][j] = 1
+
+    # print(startPos)
+    # print(targetPosList)
+
+    for target_pos in targetPosList:
+        min_dist = BFS(target_pos)
+        # print(min_dist)
+        ans += min_dist - 1
+    print(ans)
+
+```
+
+너무 전형적인 BFS 문제였습니다.