Editing Persistent data structure (section)

====Complexity of fat node====
With using fat node method, it requires O(1) space for every modification: just store the new data. Each modification takes O(1) additional time to store the modification at the end of the modification history. This is an [[Amortized analysis|amortized time]] bound, assuming modification history is stored in a growable [[Array data structure|array]]. At [[access time]], the right version at each node must be found as the structure is traversed. If "m" modifications were to be made, then each access operation would have O(log m) slowdown resulting from the cost of finding the nearest modification in the array.