computeCount method
计算当前节点的后代节点数
Implementation
int computeCount() {
eachAfter((T node, b, c) {
int sum = 0;
List<T> children = node._childrenList;
int i = children.length;
if (i == 0) {
sum = 1;
} else {
while (--i >= 0) {
sum += children[i]._count;
}
}
node._count = sum;
return false;
});
return _count;
}