有dalao能告诉我为什么RE吗？ （大一蒟蒻新生只学了c看不太懂题解的cpp代码

#include<stdio.h>
int main()
{
	long long a[200001]={0},frequency[200001]={0};
	long long ans=0;
	int n;
	long long c;
	scanf("%d %ld",&n,&c);
	for(size_t i = 0; i < n; i++)
	{
		scanf("%d",&a[i]);
		frequency[a[i]]++;
		a[i] -= c;
	}
	for(size_t i = 0; i < n; i++)
	{
		if(a[i]>=0 && a[i]<200000)
		ans += frequency[a[i]];
	}
	printf("%ld",ans);
	return 0;
}