LeetCode 38.Count and Say

     a[1]="1";
for(int i=2;i<=30;i++)
{
    char s1=a[i-1][0];int num=1;
    string str="";
    for(int j=1;j<a[i-1].size();j++)
    {
        if(a[i-1][j]!=a[i-1][j-1])
        {
            char x = num+'0';
            str+=x;
            str+=s1;
            
            num=1;
            s1=a[i-1][j];
            continue;
        }
        else
            num++;
    }
    char x = num+'0';
    str += x;
    str += s1;
    
    a[i]=str;
}
    
    return a[n];
}