Explanation of the taste of snow vegetables -- searching for Literature

【 Deep base 18. example 3】 Search for Literature - Luogu

label ：bfs、dfs、 graph theory 、 The template questions

Ideas ： Grand classic graph dfs and bfs, But here is a special case , It requires rules from small to large to search , So we need to sort first , Preprocess something , See code for details

#include<bits/stdc++.h>
using namespace std;
typedef unsigned long long ULL;
typedef long long LL;

const int N=1000010;
int h[N],e[N],ne[N],idx;
bool st[N];  //  Weight array , Judge whether the current node has been traversed , Prevent repeated traversal 

struct node{
      // Defining structure , Used to give the order of connection of edges , Sort 
	int x,y;
}arr[N];

void add(int a,int b){
    
	e[idx]=b;
	ne[idx]=h[a];
	h[a]=idx++;
}

bool cmp(node a,node b){
      // Prioritize   Small node 
	if(a.x!=b.x){
             // Then how can a point have multiple edges , We should put the big ones in front , Why? ？
		return a.x<b.x;   //  because ,add() It's head insertion , So in reverse order , You can draw a picture to understand 
	}else{
    
		return a.y>b.y;
	}
}

void dfs_map(int u){
    
    st[u]=true;
	cout<<u<<' ';
	for(int i=h[u];i!=-1;i=ne[i]){
    
		int j=e[i];
		if(!st[j]){
    
			dfs_map(j);
		}
	}
	
}

//  Next is the general graph bfs and dfs The board is broken 
void bfs_map(){
    
    memset(st,0,sizeof st);	
	
	queue<int> que;
    st[1]=true;
	que.push(1);
	while(!que.empty()){
    
		auto t=que.front();
		que.pop();
		cout<<t<<' ';
		
		for(int i=h[t];i!=-1;i=ne[i]){
    
			int j=e[i];
			
			if(!st[j]){
    
				st[j]=true;
				que.push(j);
			}
			
		}
	}
	
}

int main(){
    
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	
	memset(h,-1,sizeof h);
	int n,m;
	cin>>n>>m;
	
	for(int i=0;i<m;i++){
    
		int a,b;
		cin>>a>>b;
		arr[i].x=a;
		arr[i].y=b;
	}
	
	sort(arr,arr+m,cmp);
	
	for(int i=0;i<m;i++){
    
// cout<<arr[i].x<<"--"<<arr[i].y<<endl;
		add(arr[i].x,arr[i].y);
	}
	
	
	dfs_map(1);
	cout<<endl;
	bfs_map();
	
}

@ I'm not very good at expressing , The algorithm is just a glimpse of the path , If you don't understand anything , Where the writing is not good , Feel free to leave a comment in the comments section , I'll learn a lesson , Improve yourself slowly , thank you ！