public class Sample {
private Object[] array;
private int[] stack;
private int sp;
public Sample(int size){
array = new Object[size];
stack = new int[size + 1];
sp = 0;
stack[0] = 0;
}
public void add(Object obj){
if(stack[sp] >= array.length) return;
array[stack[sp]] = obj;
if(sp == 0){
stack[sp]++;
}else{
sp--;
}
}
public Object get(int index){
if(index >= 0 && index < array.length){
return array[index];
}else{
return null;
}
}
public Object remove(int index){
if(index < 0 || index >= array.length || array[index] == null) return null;
Object obj = array[index];
array[index] = null;
stack[++sp] = index;
return obj;
}
public void defrag(){
int ptr = stack[0] - 1;
while(sp > 0 && ptr >= 0){
if(array[ptr] != null){
if(stack[sp] < ptr){
Object tmp = array[ptr];
array[ptr] = array[stack[sp]];
array[stack[sp]] = tmp;
ptr--;
}
sp--;
}else{
ptr--;
}
}
sp = 0;
stack[0] = ptr >= 0 ? ptr + 1 : 0;
}
}