题解 | #迷宫问题#
迷宫问题
https://www.nowcoder.com/practice/cf24906056f4488c9ddb132f317e03bc
思路分析
本题迷宫只有一条通道,可以使用DFS,栈内元素正好为所走的路径,也是最短路径。
若迷宫不只一条通道,使用DFS走通的路径不一定是最短路径,最好采用BFS。
方法一:DFS
def DFS(start): stack = [] stack.append(start) maze[0][0] = 2 # 走过标记为2 while stack: if stack[-1] == end: # 栈内元素为所走的路径 for i in stack: print(f"({i[0]},{i[1]})") break r, c = stack[-1] neighbors = [(r - 1, c), (r, c + 1), (r + 1, c), (r, c - 1)] # (r,c)的邻居 for neighbor in neighbors: i, j = neighbor if 0 <= i < N and 0 <= j < M: # 有效邻居 if maze[i][j] == 0: stack.append((i, j)) maze[i][j] = 2 # 走过标记为2 break else: # 无路可走,回退 stack.pop() # 0.输入 N, M = map(int, input().split()) maze = [list(map(int, input().split())) for _ in range(N)] # 1.起点与终点 start = (0, 0) end = (N-1, M-1) # 2.DFS DFS(start)
方法二:BFS
def BFS(start): queue = [] queue.append(start) visited = set() visited.add(start) father[(0, 0)] = (-1, -1) # 任取(0,0)上一步(-1,-1) while queue: (r, c) = queue.pop(0) if (r, c) == end: return for i, j in [(r - 1, c), (r, c + 1), (r + 1, c), (r, c - 1)]: if 0 <= i < N and 0 <= j < M: if maze[i][j] == 0 and (i, j) not in visited: queue.append((i, j)) visited.add((i, j)) father[(i, j)] = (r, c) # 0.输入 N, M = map(int, input().split()) maze = [list(map(int, input().split())) for _ in range(N)] # 1.起点与终点 start = (0, 0) end = (N-1, M-1) # 2.BFS后得出路径坐标的映射关系 father = {} # 收集坐标与上一步映射关系,用字典来表示 BFS(start) # 3.路径倒推 path = [] while end != (-1, -1): path.append(end) end = father[end] for p in path[::-1]: # 路径的逆序,按格式输出 print(f"({p[0]},{p[1]})")#题解##迷宫##BFS##DFS#