AW344 观光之旅

题目地址

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易错点：

• 如果要将k改为k-1则需要保证全部改完，否则就会出现严重错误.
• 获取最小环时j应当大于i，由对称性可知最终可求出正确答案.
• 环的性质是dis[i][j]+a[j][k]+a[k][i]，即呈环状.
• 需要开long long.

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#include<cstdio>
#include<iostream>
#include<cstring>
#include<vector>
#define ll long long
using namespace std;
const int MAXN=1e3,MAXM=2e4,INF=0x3f3f3f3f;
vector<int> nowPath;
int pos[MAXN][MAXN];
void getPath(int a,int b){
	if(!pos[a][b])return;
	int k=pos[a][b];
	getPath(a,k);
	nowPath.push_back(k);
	getPath(k,b);
}
int a[MAXN][MAXN],dis[MAXN][MAXN];
int main(){
	memset(a,0x3f,sizeof(a));
	int n,m;
	scanf("%d%d",&n,&m);
	for(int i=1;i<=n;i++)
		a[i][i]=0;
	for(int i=1;i<=m;i++){
		int u,v,w;
		scanf("%d%d%d",&u,&v,&w);
		a[u][v]=a[v][u]=min(w,a[u][v]);
	}
	memcpy(dis,a,sizeof(a));
	int minLength=INF;
	for(int k=1;k<=n;k++){
		for(int i=1;i<=n;i++){
			for(int j=1;j<=n;j++){
				if(dis[i][j]>dis[i][k-1]+dis[k-1][j]){
					dis[i][j]=dis[i][k-1]+dis[k-1][j];
					pos[i][j]=k-1;
				}
			}
		}
		for(int i=1;i<=n;i++){
			if(i!=k)
			for(int j=i+1;j<=n;j++){
				if(j!=k){
					if((ll)dis[i][j]+a[j][k]+a[k][i]<minLength){
						minLength=dis[i][j]+a[j][k]+a[k][i];
						nowPath.clear();
						nowPath.push_back(i);
						getPath(i,j);
						nowPath.push_back(j);
						nowPath.push_back(k);
					}
				}
			}
		}
	}
	if(minLength==INF){
		printf("No solution.\n");
		return 0;
	}
	for(int i=0;i<nowPath.size();i++){
		printf("%d ",nowPath.at(i));
	}
	printf("\n");
	return 0;
}