TLE|WA;代码

TLE代码,正常的双层循环

#include<iostream>
#include<string>
using namespace std;
string s;char a1,a2;int k;
int main(){
	cin>>k;
	cin>>s>>a1>>a2;
	int count=0,n=s.length();
	if(s.find(a1)==-1||s.find(a2)==-1){cout<<0;return 0;}
	for(int i=s.find(a1);i<n;i++)for(int j=i+k-1;j<n;j++)if(s[i]==a1&&s[j]==a2)count++;
	cout<<count;
	return 0;
}

WA+TLE代码,双指针

#include<iostream>
#include<bits/stdc++.h>
using namespace std;
int k;string s;char a1,a2;
int a[550005],tot=0,b[550005],len=0,sum=0,l=0,r=0,h=0;
int main()
{
	cin>>k>>s>>a1>>a2;
	for(int i=0;i<s.size();i++)if(s[i]==a1)a[++tot]=i;
	for(int i=0;i<s.size();i++)if(s[i]==a2)b[++len]=i;
	l=1,r=len;
	while(l<=tot)
	{
		if(r<=0) r=len,l++,h=1;
		if(b[r]-a[l]+1>=k) sum++;
		if(b[r]-a[l]+1<k) r=len,l++,h=1;
		if(h==0) r--;
		else h=0;
	}
	cout<<sum;
	return 0;
}

双指针哪里有问题?