Cracking the Coding Interview, 4 Edition - 150 Programming Interview Questions and Solutions

Solutions to Chapter 13 | C++
13.8 Write a method that takes a pointer to a Node structure as a parameter and returns
a complete copy of the passed-in data structure. The Node structure contains two
pointers to other Node structures.
SOLUTION
pg 76
The algorithm will maintain a mapping from a node address in the original structure to the
corresponding node in the new structure. This mapping will allow us to discover previously
copied nodes during a traditional depth first traversal of the structure. (Traversals often mark
visited nodes--the mark can take many forms and does not necessarily need to be stored in
the node.) Thus, we have a simple recursive algorithm:
1 typedef map NodeMap;
2
3 Node * copy_recursive(Node * cur, NodeMap & nodeMap) {
4 if(cur == NULL) {
5 return NULL;
6 }
7 NodeMap::iterator i = nodeMap.find(cur);
8 if (i != nodeMap.end()) {
9 // we’ve been here before, return the copy
10 return i->second;
11 }
12 Node * node = new Node;
13 nodeMap[cur] = node; // map current node before traversing links
14 node->ptr1 = copy_recursive(cur->ptr1, nodeMap);
15 node->ptr2 = copy_recursive(cur->ptr2, nodeMap);
16 return node;
17 }
18 Node * copy_structure(Node * root) {
19 NodeMap nodeMap; // we will need an empty map
20 return copy_recursive(root, nodeMap);
21 }
22
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