【Tai_mount】算法学习 - 搜索 - DFS

DFS即深度优先搜索

板子

//Dfs板子

void dfs(int x){
	if(x>n){solve();return;}
	for(int i=1;i<=n;++i) if(check(x,i)){
		arr[x]=i; book(x,i,true);
		dfs(x+1);
		book(x,i,false);
	}
	return;
} 

题目

luoguP2392 kkksc03考前临时抱佛脚

//https://www.luogu.com.cn/problem/P2392
#include<iostream>
using namespace std;
const int N=30;
int s[5],sum[5],ans;
int tim[5][N],maxx[5],thesum;
void ciin(){
	for(int i=1;i<=4;i++) cin>>s[i];
	for(int i=1;i<=4;i++) for(int j=1;j<=s[i];j++){
		cin>>tim[i][j];
		sum[i]+=tim[i][j];
	}
}
bool check(int sub,int x,int i){
	if(sum[sub]/2<thesum+i*tim[sub][x]) return false;
	return true;
}
void book(int a){
	thesum+=a;
	return;
}
void solve(int sub){
	if(maxx[sub]==0||maxx[sub]<thesum) maxx[sub]=thesum;
} 
void dfs(int sub,int x){
	if(x>s[sub]){solve(sub);return;}
	for(int i=0;i<=1;i++)if(check(sub,x,i)){
		book(i*tim[sub][x]);
		dfs(sub,x+1);
		book(-i*tim[sub][x]); 
	}
	return;
}
int main(){
	ciin();
	for(int i=1;i<=4;i++){
		dfs(i,1);
		ans+=sum[i]-maxx[i];
	}
	cout<<ans;
	return 0;
} 

luoguP1219 [USACO1.5]八皇后 Checker Challenge

//https://www.luogu.com.cn/problem/P1219
#include<iostream>
using namespace std;
const int M=20;
int n,arr[M],cnt;
bool a[M],b[M],c[M];
void ciin(){
	cin>>n;
}
void solve(){
	cnt++;
	if(cnt<=3){
		for(int i=1;i<=n;i++){
			cout<<arr[i]<<' ';
		}
		cout<<'\n';
	}
}
bool check(int x,int i){
	if(a[i]||b[i+x]||c[20+i-x]){return false;}
	return true;
}
bool book(int x,int i,bool tf){
	a[i]=tf;b[i+x]=tf;c[20+i-x]=tf;
}
void dfs(int x){
	if(x>n){solve();return;}
	for(int i=1;i<=n;i++) if(check(x,i)){
		arr[x]=i; book(x,i,true);
		dfs(x+1);
		book(x,i,false);
	}
}
int main(){
	ciin();
	dfs(1);
	cout<<cnt;
	return 0;
}