为什么会RE?

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int INF=0x3f3f3f3f;
const int MOD=998244353;
const int N=200005;
int p[N],b[N],ans[N];
vector<int> a[N];
set<int> s;
inline int read(){
	int w=0,f=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){
		if(ch=='-') f=-1;
		ch=getchar();
	}
	while(ch>='0'&&ch<='9'){
		w=(w<<1)+(w<<3)+(ch-48);
		ch=getchar();
	}
	return w*f;
}
inline int Pow(int a,int b){
	int ans=1;
	for(;b;b>>=1){
		if(b&1) ans=(ans*a)%MOD;
		a=(a*a)%MOD;
	}
	return ans;
}
signed main(){
	int n,k,m=0;
	n=read();k=read();
	for(int i=1;i<=n;i++) p[i]=read();
	for(int i=1;i<=n;i++){
		auto x=s.lower_bound(p[i]);
		if(x==s.end()){
			a[++m].push_back(p[i]);
			s.insert(p[i]);
			b[p[i]]=m;
		}
		else{
			a[b[(*x)]].push_back(p[i]);
			s.erase(x);
			s.insert(p[i]);
			b[p[i]]=b[(*x)]; //Here gonna be RE.why?
		}
		if((int)(a[b[p[i]]].size())>=k){
			s.erase(p[i]);
			for(auto u : a[b[p[i]]]) ans[u]=i;
		}
	}
	for(int i=1;i<=n;i++){
		if(ans[i]==0) printf("-1\n");
		else printf("%lld\n",ans[i]);
	}
    return 0;
}