代码随想录算法训练营第56天 | 广搜和深搜应用

110.字符串接龙
https://kamacoder.com/problempage.php?pid=1183
代码随想录
https://www.programmercarl.com/kamacoder/0110.字符串接龙.html#思路
105.有向图的完全可达性
https://kamacoder.com/problempage.php?pid=1177
代码随想录
https://www.programmercarl.com/kamacoder/0105.有向图的完全可达性.html
106.岛屿的周长
https://kamacoder.com/problempage.php?pid=1178
代码随想录
https://www.programmercarl.com/kamacoder/0106.岛屿的周长.html#思路

110.字符串接龙

• step1：根据字符串建立图（邻接表）；

• step2：无向图求最短路径：广度优先搜索；

• 广搜逻辑：

  • 一定要用队列：先进先出；
  点击查看代码

  from collections import deque
  
  def main():
  	dict_num = int(input())
  	source,target = input().split()
  	dict_str = [source]
  	for i in range(dict_num):
  		dict_str.append(input())
  	dict_str.append(target)
  	path_li = {}
  	for i in range(len(dict_str)):
  		path_li[i] = []
  		for j in range(len(dict_str)):
  			if i==j:
  				continue
  			if pre_distance(dict_str[i],dict_str[j])==1:
  				path_li[i].append(j)
  	res = bfs_path(path_li,0,dict_num+1)
  	print(res)
  
  def bfs_path(graph,start,end):
  	queue = deque([(start,[start])])
  	visited = set()
  	while queue:
  		node,path =  queue.popleft()
  		if node==end:
  			return len(path)
  		if node not in visited:
  			visited.add(node)
  			if len(graph[node])==0:
  				break
  				return 0
  			for neighbor in graph[node]:
  				if neighbor not in visited:
  					queue.append((neighbor,path+[neighbor]))
  	return []
  
  def pre_distance(str1,str2):
  	distance = 0
  	for i in range(len(str1)):
  		if str1[i]!=str2[i]:
  			distance+=1
  	return distance
  
  
  if __name__ == '__main__':
  	main()
  

105.有向图的完全可达性

• 两种方式进行深搜：

  • 当前值执行；
  当前值执行

  def main():
  	n,k = map(int,input().split())
  	graph = {i:[] for i in range(n+1)}
  	for i in range(k):
  		s,t = map(int,input().split())
  		graph[s].append(t)
  	visited = [0]*(n+1)
  	dfs(graph,visited,1)
  	for i in range(1,n+1):
  		if visited[i]==0:
  			print("-1")
  			return
  	print("1")
  
  
  def dfs(graph,visited,node):
  	if visited[node]==1:
  		return
  	visited[node] =1
  	if len(graph[node])!=0:
  		for key in graph[node]:
  			dfs(graph,visited,key)
  
  if __name__ == '__main__':
  	main()
  

  • 处理过当前值循环；（和BFS的位置相同）
  处理过当前值循环

  from collections import deque
  def main():
  	n,k = map(int,input().split())
  	graph = {i:[] for i in range(n+1)}
  	for i in range(k):
  		s,t = map(int,input().split())
  		graph[s].append(t)
  	visited = [0]*(n+1)
  	visited[1] = 1
  	bfs(graph,visited,1)
  	for i in range(1,n+1):
  		if visited[i]==0:
  			print("-1")
  			return
  	print("1")
  
  def dfs(graph,visited,node):
  	visited[node] =1
  	if len(graph[node])!=0:
  		for key in graph[node]:
  			if visited[key]==0:
  				dfs(graph,visited,key)
  def bfs(graph,visited,node):
  	queue = deque([node])
  	while queue:
  		curr =queue.popleft()
  		for key in graph[curr]:
  			if visited[key]==0:
  				visited[key]=1
  				queue.append(key)
  
  if __name__ == '__main__':
  	main()
  

106. 岛屿的周长

• 统计岛屿的周长；

• 方法一：所有块的数量4-重合数量2

  点击查看代码

  def main():
  	n,m = map(int,input().split())
  	graph = [[0]*m for _ in range(n)]
  	for i in range(n):
  		data = input().split()
  		for j in range(m):
  			graph[i][j] = int(data[j])
  
  	directions = [[0,1],[0,-1]]
  	bound = 0
  	combine = 0
  	for i in range(n):
  		for j in range(m):
  			if graph[i][j]==1:
  				bound+=1
  				if i-1>=0 and graph[i-1][j]==1:
  					combine+=1
  				if j-1>=0 and graph[i][j-1]==1:
  					combine+=1
  	print(str(bound*4-combine*2))
  
  if __name__ == '__main__':
  	main()
  

• 方法二：遇到了边缘块 统计边缘数量即可

  点击查看代码

  def main():
  	n,m = map(int,input().split())
  	graph = [[0]*m for _ in range(n)]
  	for i in range(n):
  		data = input().split()
  		for j in range(m):
  			graph[i][j] = int(data[j])
  
  	directions = [[0,1],[0,-1],[1,0],[-1,0]]
  	bound = 0
  	for i in range(n):
  		for j in range(m):
  			if graph[i][j]==1:
  				for dir_ in directions:
  					nextx = i+dir_[0]
  					nexty = j+dir_[1]
  					if nextx<0 or nextx>=len(graph) or nexty<0 or nexty>=len(graph[0]):
  						bound+=1
  					elif graph[nextx][nexty]==0:
  						bound+=1
  					else:
  						continue
  	print(bound)
  
  if __name__ == '__main__':
  	main()