Spoj is it a tree

//http://www.spoj.com/problems/PT07Y/

#include<stdio.h>
struct set{
int parent;
int rank;
};
int find(struct set ar[],int a){
if(ar[a].parent==-1){
return a;
}
find(ar,ar[a].parent);
}
int main(){
int a,b,c,d,e,x,i=0;
scanf("%d %d",&a,&b);
struct set ar[a+1];
for(x=0;x<=a;x++){
ar[x].parent=-1;
ar[x].rank=0;
}
while(b--){
scanf("%d %d",&c,&d);
int g=find(ar,c);
int f=find(ar,d);
if(g==f){
i=1;
}else{
if(ar[g].rank<ar[f].rank)
        ar[g].parent=f;
    else if(ar[g].rank>ar[f].rank)
        ar[f].parent=g;
    else{
        ar[f].parent=g;
        ar[g].rank++;
    }
}
}
if(i==0){
printf("YES\n");
}else{
printf("NO\n");
}
return 0;
}