java: use StringBuilder to insert at the beginning

Solution 1:

StringBuilder sb = new StringBuilder();
for(int i=0;i<100;i++){
    sb.insert(0, Integer.toString(i));
}

Warning: It defeats the purpose of StringBuilder, but it does what you asked.

Better technique (although still not ideal):

1. Reverse each string you want to insert.
2. Append each string to a StringBuilder.
3. Reverse the entire StringBuilder when you're done.

This will turn an O(n²) solution into O(n).

Solution 2:

you can use strbuilder.insert(0,i);

Solution 3:

Maybe I'm missing something but you want to wind up with a String that looks like this, "999897969594...543210", correct?

StringBuilder sb = new StringBuilder();
for(int i=99;i>=0;i--){
    sb.append(String.valueOf(i));
}