Tree matching

input/code.cpp: In function 'll cnt(ll, ll*, ll*)':
input/code.cpp:9:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(c[i][0]!=-1)cnt(c[i][0],a,a+1);
                ^
input/code.cpp:10:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(c[i][1]!=-1)cnt(c[i][1],b,b+1);
                ^
input/code.cpp: In function 'int main()':
input/code.cpp:18:19: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%llu",&n);
                   ^
input/code.cpp:20:37: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%llu %llu",c[i]+0,c[i]+1);
                                     ^

#include <stdio.h>
typedef unsigned long long N;
typedef N ll;
const ll M=1e9+7;
ll c[101010][2];
ll cnt(ll i,ll* x, ll* y){
  *x=1,*y=0;
  ll a[2]={0,1},b[2]={0,1};
  if(c[i][0]!=-1)cnt(c[i][0],a,a+1);
  if(c[i][1]!=-1)cnt(c[i][1],b,b+1);
  *x=(a[1]*b[1])%M;
  *y=(*x+((a[0]*b[1])%M+(b[0]*a[1])%M)%M)%M;
  //printf("%llu: %llu %llu\n",i,*x,*y);
  return *y;
}
int main(){
  N n,i;
  scanf("%llu",&n);
  for(i=0;i<n;++i){
    scanf("%llu %llu",c[i]+0,c[i]+1);
    --c[i][0],--c[i][1];
  }
  printf("%llu\n",cnt(0,&n,&i));
  return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: RUNTIME ERROR

Test 3

Verdict: RUNTIME ERROR

Test 4

Verdict: RUNTIME ERROR

Test 5

Verdict: RUNTIME ERROR

Test 6

Verdict: RUNTIME ERROR

Test 7

Verdict: RUNTIME ERROR