HDU 1325 Is It A Tree?

题意

思路

传送门

#include <cstdio>
#include <cstring>
#include <iostream>

using namespace std;

class UnionFind {
private:
int * fa;
int size;
public:
UnionFind(int n) {
size = n;
fa = new int[n+1];
Init();
}

~UnionFind() {
delete[] fa;
}

void Init() {
for(int i = 1 ; i <= size ; i ++) {
fa[i] = i;
}
}

int Find(int x) {
if(fa[x] != x) {
fa[x] = Find(fa[x]);
}
return fa[x];
}

bool Union(int x,int y) {
int fx = Find(x);
int fy = Find(y);
if(fx != fy) {
fa[fx] = fy;
return true;
}
else {
return false;
}
}

int GetCount() {
int count = 0;
for(int i = 1 ; i <= size ; i ++) {
if(fa[i] == i) {
count ++;
}
}
return count;
}
};

#define MAXN 1000005

bool vis[MAXN+1];
int indegree[MAXN+1];

int main() {
int u,v;
int cnt = 0;
UnionFind uf(MAXN);
memset(vis,0,sizeof(vis));
bool haveCircle = false;
int indegreeZeroNum = 0;

while(~scanf("%d %d",&u,&v)) {
if(u < 0 && v < 0) {
break;
}
if(u == 0 && v == 0) {
int tmpcnt = 0;
for(int i = 1 ; i <= MAXN ; i++) {
if(vis[i]) {
tmpcnt ++;
if(indegree[i] == 0) {
// printf("%d\n", i);
indegreeZeroNum ++;
}
}
}
// printf("%d\n", indegreeZeroNum);
if(indegreeZeroNum == 1 && haveCircle == false && uf.GetCount() + tmpcnt == MAXN + 1) {
printf("Case %d is a tree.\n",++cnt);
}
else {
printf("Case %d is not a tree.\n",++cnt);
}
uf.Init();
memset(vis,0,sizeof(vis));
memset(indegree,0,sizeof(indegree));
indegreeZeroNum = 0;
haveCircle = false;
}
else {
vis[u] = true;
vis[v] = true;
indegree[v] ++;
if(false == uf.Union(u,v)) {
haveCircle = true;
}
}
}
return 0;
}