HELP NEEDED

help
,
1

Can someone help me to find out why my code is giving wrong answers :

Question link :: here

Code ::

class Solution {

bool isSubSequence(string str1, string str2,int m,int n)
{

    if (m == 0)
        return true;
    if (n == 0)
        return false;

    if (str1[m - 1] == str2[n - 1])
        return isSubSequence(str1, str2, m - 1, n - 1);

    return isSubSequence(str1, str2, m, n - 1);
}

int dp[1009];

int solve(vector<string>&a,int in,string s)
{
    if(in == a.size())
    return 0;

    
     if(dp[in]!=-1)
        return dp[in];
 
    
    if(s.size()==0)
     return dp[in]=max(1+solve(a,in+1,a[in]),solve(a,in+1,s));
      

        string s1=a[in];
    if((isSubSequence(s, s1,s.size(),s1.size())==true)&&(s1.size()-s.size()==1))
    {
       // cout<<s<<" "<<a[in]<<endl;
            return dp[in]=max(1+solve(a,in+1,a[in]),solve(a,in+1,s));
    }
    
    
       else
       {
              
          return dp[in]=solve(a,in+1,s);
       }
    
         
}

static bool bylength(string &s1, string &s2){
    return s1.length()<s2.length();
}

public:
int longestStrChain(vector& a) {

    sort(a.begin(), a.end(),bylength);
       int n=a.size(),i;
   //for(i=0;i<n;i++)cout<<a[i]<<" ";
     memset(dp,-1,sizeof(dp));
    
 
       string s="";
    
   int x=solve(a,0,s);
    
  
    
    return x;
    
    
}

};