SGU 101. Domino 欧拉回路

无向图欧拉回路 欧拉通路

#include <cstdio>
#include <cstring>
using namespace std;

struct edge
{
	int v, next, b, id;
}e[210];
int vis[210];
int first[10], cnt;
int ans[210], len;

int f[10];

int find(int x)
{
	if(x != f[x])
		return f[x] = find(f[x]);
	return f[x];
}
void AddEdge(int u, int v, int id)
{
	e[cnt].id = id;
	e[cnt].b = 0;
	e[cnt].v = v;
	e[cnt].next = first[u];
	first[u] = cnt++;

	e[cnt].id = id;
	e[cnt].b = 1;
	e[cnt].v = u;
	e[cnt].next = first[v];
	first[v] = cnt++;
}

void dfs(int u)
{
	for(int i = first[u]; i != -1; i = e[i].next)
	{
		if(!vis[i])
		{
			vis[i] = 1;
			vis[i^1] = 1;
			dfs(e[i].v);
			ans[len++] = i;
		}
	}
}
int main()
{
	int n;
	scanf("%d", &n);
	memset(first, -1, sizeof(first));
	cnt = 0;
	int b[10] = {0}, s1 = 0, s2 = 0;
	for(int i = 0; i <= 6; i++)
		f[i] = i;
	for(int i = 1; i <= n; i++)
	{
		int u, v;
		scanf("%d %d", &u, &v);
		AddEdge(u, v, i);
		if(!b[u])
		{
			s1++;
			b[u] = 1;
		}
		else
			b[u]++;
		if(!b[v])
		{
			s1++;
			b[v] = 1;
		}
		else
			b[v]++;
	 	int x = find(u), y = find(v);
	 	if(x != y)
 		{
		 	f[x] = y;
		 	s2++;
 		}
	}

	int rt = -1, sum = 0;
	len = 0;
	for(int i = 0; i <= 6; i++)
	{
		if(b[i]&1)
		{
			sum++;
			rt = i;
		}
	}
	if(s1 - 1 != s2)
	{
		puts("No solution");
	}
	else if(sum == 2)
	{
		dfs(rt);
		for(int i = len-1; i >= 0; i--)
		{
			int x = ans[i];
			if(e[x].b)
				printf("%d -\n", e[x].id);
			else
				printf("%d +\n", e[x].id);
		}
	}
	else if(!sum)
	{
		for(int i = 0; i <= 6; i++)
		{
			if(b[i])
			{
				dfs(i);
				break;
			}
		}
		for(int i = len-1; i >= 0; i--)
		{
			int x = ans[i];
			if(e[x].b)
				printf("%d -\n", e[x].id);
			else
				printf("%d +\n", e[x].id);
		}
	}
	else
		puts("No solution");
	return 0;
}