Ositus

#include<iostream>
#include<string>
#include<vector>
#include<unordered_map>
using namespace std; 
 
int main(){
    int MOD =1e9+7; 
    long long int i, j; 
    string s; 
    long long int ans=1;
    cin>>s; 
    int n= s.length();
    long long int v[n];
    unordered_map<char, int> m; 
    long long int r=-1; 
    bool ry=false; 
    v[0]=1;
    m[s[0]]=0;
    for(i=1; i<n; i++)
    {
        if(m[s[i]]==0&&s[i]!=s[0]){
            if(ry){
                for( j=i-2; j>=r; j--){
                    ans+=v[j];
                    ans%=MOD;}
            }
            else{
            for(j=i-2;j>r; j--){
                ans+=v[j];
                ans%=MOD;}
            }
            if(r==-1){
                ans+=1;
                ans%=MOD;
            }
            m[s[i]]=i;
            v[i]=ans;
        
        }
        else{
            ry=true; 
            if(m[s[i]]>r){
                r=m[s[i]];
                for(j=i-2;j>=r; j--){
                ans+=v[j];
                ans%=MOD;}
            }
            else{
                for(j=i-2;j>=r; j--){
                ans+=v[j];
                ans%=MOD;}
            }
            m[s[i]]=i;
            v[i]=ans;
 
 
            }
 
        }
 
    
        
    
    cout<<ans;
}

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 1, 2, 3

Verdict: ACCEPTED

Test 3

Group: 1, 2, 3

Verdict: ACCEPTED

Test 4

Group: 1, 2, 3

Verdict: ACCEPTED

Test 5

Group: 2, 3

Verdict: ACCEPTED

Test 6

Group: 3

Verdict: ACCEPTED

Test 7

Group: 3

Verdict: ACCEPTED