洛谷 #5022. 旅行

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题意

从1出发，遍历一棵树，使dfs序最小

可能有n条边

题解

贪心，每次向最小的节点走

调试记录

被卡常。

#include <cstdio>
#include <queue>
#include <vector>
#include <cstring>
#include <algorithm>
#define maxn 5005
using namespace std;
struct Enode{
	int u, v;
}e[maxn];
//result node
struct ResNode{
	int res[maxn], cnt;
	void reset(){
		cnt = 0;
		memset(res, 0, sizeof res);
	}
	bool operator <(ResNode x)const{
		for (int i = 1; i <= cnt; i++)
			if (res[i] < x.res[i]) return true;
			else if (res[i] > x.res[i]) return false;
		return false;
	}
	ResNode operator =(ResNode x){
		for (int i = 1; i <= cnt; i++)
			res[i] = x.res[i];
		cnt = x.cnt;
		return *this;
	}
}res, ans;
//find way
vector <int> E[maxn];
int n, m;
bool vis[maxn], tag[maxn << 1], flag;
void dfs(int cur, int u1, int v1){
	if (res.cnt >= n) return;
	
	if (vis[cur]) return;
	vis[cur] = true;
	
	if (cur > ans.res[res.cnt + 1] && !flag) return;
	else if (cur < ans.res[res.cnt + 1]) flag = true;
	res.res[++res.cnt] = cur;
	
    for (int i = 0; i < E[cur].size(); i++){
		if (cur == u1 && E[cur][i] == v1) continue;
		if (cur == v1 && E[cur][i] == u1) continue;
    	if (!vis[E[cur][i]]) dfs(E[cur][i], u1, v1);
    }
}
int main(){
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= m; i++){
        scanf("%d%d", &e[i].u, &e[i].v);
       	E[e[i].u].push_back(e[i].v), E[e[i].v].push_back(e[i].u);
    }
    for (int i = 1; i <= n; i++) sort(E[i].begin(), E[i].end());
    if (m == n - 1){
    	for (int i = 1; i <= n; i++)
    		ans.res[i] = n - i + 1;
    	res.reset();
        dfs(1, 0, 0);
        for (int i = 1; i <= n; i++)
            printf("%d ", res.res[i]);
        putchar('\n');
    }
    if (m == n){
    	for (int i = 1; i <= n; i++)
    		ans.res[i] = n - i + 1;
    	ans.cnt = n;
        for (int i = 1; i <= n; i++){
        	flag = false;
        	memset(vis, false, sizeof vis);
        	res.reset();
        	dfs(1, e[i].u, e[i].v);
        	if (res.cnt == n){
        		if (res < ans) ans = res;
			}
		}
		for (int i = 1; i <= n; i++)
            printf("%d ", ans.res[i]);
        putchar('\n');
    }
    return 0;
}