private FenwickTreeNode ParseArrayIntoFenwickTreeHelper(int[] array, int lower, int upper)
{
if (lower > upper)
{
return(null);
}
if (lower == upper)
{
return(new FenwickTreeNode
{
lower = lower,
upper = upper,
value = array[lower],
});
}
var node = new FenwickTreeNode
{
lower = lower,
upper = upper,
left = ParseArrayIntoFenwickTreeHelper(array, lower, (upper + lower) / 2),
right = ParseArrayIntoFenwickTreeHelper(array, (upper + lower) / 2 + 1, upper),
};
node.value = (node.left == null ? 0 : node.left.value) + (node.right == null ? 0 : node.right.value);
return(node);
}
private int QueryAndUpdateFenwickTree(int value, FenwickTreeNode head, int[] valueIndexArray, int currentEmptySlot)
{
var index = valueIndexArray[value];
var result = Query(head, 0, index);
Update(head, index, 0);
Update(head, currentEmptySlot, 1);
valueIndexArray[value] = currentEmptySlot;
return(result);
}
private int Query(FenwickTreeNode head, int lower, int upper)
{
if (head == null)
{
return(0);
}
if (head.lower == lower && head.upper == upper)
{
return(head.value);
}
if (upper <= head.left.upper)
{
return(Query(head.left, lower, upper));
}
else
{
return(Query(head.left, lower, head.left.upper) + Query(head.right, head.right.lower, upper));
}
}
private void Update(FenwickTreeNode head, int index, int value)
{
if (head == null)
{
return;
}
if (head.upper == index && head.lower == index)
{
head.value = value;
return;
}
if (index <= (head.upper + head.lower) / 2)
{
Update(head.left, index, value);
}
else
{
Update(head.right, index, value);
}
head.value = (head.left == null ? 0 : head.left.value) + (head.right == null ? 0 : head.right.value);
}