1. And DFS Similarities and differences

The same thing ： Search for all possible states .

Difference ： Search order .

2. BFS Always search the state close to the initial state first , It is according to ： Start state -> All states that can be reached with just one transition -> All states that can be reached with just two transitions ->……

Search for the same state only once , So the complexity is O（ Number of States * Transfer mode ）.

3. DFS Implicit use of the stack , and BFS Using queues , When searching, first queue the initial state , After that, get out of the team , And queue the state that can be transferred to the state that has not been accessed ,

Repeat the process , Until the queue is empty or a solution is found . Looking at the queue, we can see that , All States are traversed from near to far from the initial state .

Here is a classic example ： The shortest path in the maze

description:
Given a size of N*M The maze of . The labyrinth is made up of passages and walls , Each step can move to the adjacent four grid channels . Request the minimum number of steps from the start to the end . Please note that , This problem assumes that you can move from the beginning to the end .

Sample input and output ：
Input ：

Output ：
22

AC Code：

```int INF=0x3f3f3f3f;
typedef pair<int,int> P;
int N,M,sx,sy,gx,gy;
char maze[N][M];
int d[N][M];// Record the shortest distance to each position
int dx[]={,,-,},dy={,,,-};
int bfs(){
queue<P> q; q.push(P(sx,sy));
memset(d,INF,sizeof(d));
d[sx][sy]=;
while(！q.empty()){
P p=q.front(); q.pop();
if(p.first ==gx&&p.second ==gy) break;
for(int i=;i<;i++){
int nx=P.first +dx[i],ny=P.second +dy[i];
if(nx>=&&nx<N&&ny>=&&ny<M&&maze[nx][ny]!='#'&&d[nx][ny]==INF){
q.push(P(nx,ny));
d[nx][ny]=d[p.first ][p.second]+;
}
}
}
return d[gx][gy];
}```

1. 【 Introduction to algorithm 】 Breadth / Width first search (BFS)

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2. Challenge the program 2.1.5 Exhaustive search &gt;&gt; Width first search

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3. 【BFS Width first search 】

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4. Step by step —— Width first search （BFS）

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5. BFS Optimization of algorithm Two way width first search

Two way width first search (Bidirectional BFS) The algorithm is suitable for the following scenarios : Undirected graph The length of all sides is 1 Or the length is the same At the same time, the starting point and the ending point are given above 3 When all conditions are met , You can use bidirectional width first ...

Breadth first search (Breadth First Search, BFS) BFS The general idea of algorithm implementation is : // BFS void BFS(int s){ queue<int> q; // Define a ...

7. [ Width first search ] FZU-2150 Fire Game

Fat brother and Maze are playing a kind of special (hentai) game on an N*M board (N rows, M columns) ...

8. Width first search -------- The shortest path problem of maze (dfs)

Width first search uses queues (queue) stay unility Header file Source code #include<iostream>#include<cstdio>#include<queue&g ...

9. Width first search （BFS）— 20180909 - 20180917

BFS Several kinds of questions : 1. Graph traversal :a. Level traversal b. From point to face c. A topological sort 2. The shortest path of a simple graph : Simple picture :1. Undirected graph 2. Edge weights are consistent Time complexity of graph : N A little bit ,M side ,M The biggest is N^2, Time complexity O(N+M ...

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