poj1308

简单题

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

#define maxn 1006

struct Edge
{
int v, next;
}edge[1000005];

int name[maxn];
int n, ecount, tot, root;
int in[maxn];
int head[maxn];
bool vis[maxn];
bool ok;

void addedge(int a, int b)
{
edge[ecount].next = head[a];
edge[ecount].v = b;
head[a] = ecount;
in[b]++;
ecount++;
}

int find(int a)
{
for (int i = 0; i < n; i++)
if (name[i] == a)
return i;
name[n++] = a;
return n - 1;
}

void dfs(int root)
{
vis[root] = true;
tot++;
for (int i = head[root]; i != -1; i = edge[i].next)
{
if (vis[edge[i].v])
{
ok = false;
return;
}
if (!ok)
return;
dfs(edge[i].v);
}
}

int main()
{
//freopen("t.txt", "r", stdin);
int t = 0;
while (1)
{
t++;
memset(in, 0, sizeof(in));
memset(head, -1, sizeof(head));
memset(vis, 0, sizeof(vis));
ecount = 0;
n = 0;
tot = 0;
ok = true;
int a, b;
scanf("%d%d", &a, &b);
if (a < 0 && b < 0)
return 0;
if (a == 0 && b == 0)
{
printf("Case %d is a tree.\n", t);
continue;
}
a = find(a);
b = find(b);
addedge(a, b);
while (1)
{
scanf("%d%d", &a, &b);
if (a == 0 && b == 0)
break;
a = find(a);
b = find(b);
addedge(a, b);
}
root = -1;
for (int i = 0; i < n; i++)
if (in[i] == 0)
root = i;
if (root >= 0)
dfs(root);
if (ok && tot == n && root >= 0)
printf("Case %d is a tree.\n", t);
else
printf("Case %d is not a tree.\n", t);
}
return 0;
}

转载于:https://www.cnblogs.com/rainydays/archive/2011/06/21/2086368.html