int decodeWays(const string& a)
{
    int na=a.size();
    int dp[na+1]={0};
    dp[0]=0;
    dp[1]=1;
    for(int i=2;i<=na;i++){
        if((a[i]<='0'+6 && a[i-1]==2) || a[i-1]=='1'){
            dp[i]+=dp[i-2];
        }

        dp[i]+= dp[i-1];
    }
    return dp[na];

}

==> move to fibonacci
int decodeWays(const string& a)
{
    int na=a.size();
    int fn_1=0;
    int fn_2=1;
    for(int i=2;i<=na;i++){
        int fn=0;
        if((a[i]<='0'+6 && a[i-1]==2) || a[i-1]=='1'){
            fn+=fn_2;
        }
        fn+=fn_1;
        fn_2=fn_1;
        fn_1=fn;
    }
    return fn_1;

}