Convert a binary tree into a two-way linked list

I remember this is a Microsoft interview question. I thought about it for a long time and did not know how to do it. I recently read other people's blogs and found an algorithm. I implemented it myself. The following describes the algorithm:

1. If left subtree exists, process the left subtree
..... 1. a) Recursively convert the left subtree to DLL.
..... 1. B) Then find inorder predecessor of root in left subtree (inorder predecessor is rightmost node in left subtree ).
..... 1. c) Make inorder predecessor as previous of root and root as next of inorder predecessor.
2. If right subtree exists, process the right subtree (Below 3 steps are similar to left subtree ).
..... 2. a) Recursively convert the right subtree to DLL.
..... 2. B) Then find inorder successor of root in right subtree (inorder successor is leftmost node in right subtree ).
..... 2. c) Make inorder successor as next of root and root as previous of inorder successor.
3. Find the leftmost node and return it (the leftmost node is always head of converted DLL ).

 

 

The following code is provided:

[Cpp]
# Include <iostream>
Using namespace std;
 
Typedef struct tree_node_s {
Int data;
Struct tree_node_s * lchild;
Struct tree_node_s * rchild;
} Tree_node_t;
 
 
Tree_node_t * changeToListUtil (tree_node_t * root ){
If (NULL = root)
Return NULL;
If (root-> lchild ){
Tree_node_t * left = changeToListUtil (root-> lchild );
While (left-> rchild ){
Left = left-> rchild;
}
Root-> lchild = left;
Left-> rchild = root;
}
If (root-> rchild ){
Tree_node_t * right = changeToListUtil (root-> rchild );
While (right-> lchild ){
Right = right-> lchild;
}
Root-> rchild = right;
Right-> lchild = root;
}
Return root;
}
 
Tree_node_t * changeToList (tree_node_t * root ){
If (NULL = root)
Return NULL;
Root = changeToListUtil (root );
While (root-> lchild)
Root = root-> lchild;
Return root;
}
 
 
Void printList (tree_node_t * head ){
While (head ){
Cout Head = head-> rchild;
}
}
 
Tree_node_t * createNode (int data ){
Tree_node_t * temp = (tree_node_t *) malloc (sizeof (tree_node_t ));
Temp-> data = data;
Temp-> lchild = NULL;
Temp-> rchild = NULL;
Return temp;
}
 
Int main (int argc, char * argv []) {
Tree_node_t * root = createNode (10 );
Root-> lchild = createNode (12 );
Root-> rchild = createNode (15 );
Root-> lchild = createNode (25 );
Root-> lchild-> rchild = createNode (30 );
Root-> rchild-> lchild = createNode (36 );
 
Tree_node_t * head = changeToList (root );
PrintList (head );
Cin. get ();
Return 0;
}

# Include <iostream>
Using namespace std;

Typedef struct tree_node_s {
Int data;
Struct tree_node_s * lchild;
Struct tree_node_s * rchild;
} Tree_node_t;

Tree_node_t * changeToListUtil (tree_node_t * root ){
If (NULL = root)
Return NULL;
If (root-> lchild ){
Tree_node_t * left = changeToListUtil (root-> lchild );
While (left-> rchild ){
Left = left-> rchild;
}
Root-> lchild = left;
Left-> rchild = root;
}
If (root-> rchild ){
Tree_node_t * right = changeToListUtil (root-> rchild );
While (right-> lchild ){
Right = right-> lchild;
}
Root-> rchild = right;
Right-> lchild = root;
}
Return root;
}

Tree_node_t * changeToList (tree_node_t * root ){
If (NULL = root)
Return NULL;
Root = changeToListUtil (root );
While (root-> lchild)
Root = root-> lchild;
Return root;
}

Void printList (tree_node_t * head ){
While (head ){
Cout Head = head-> rchild;
}
}

Tree_node_t * createNode (int data ){
Tree_node_t * temp = (tree_node_t *) malloc (sizeof (tree_node_t ));
Temp-> data = data;
Temp-> lchild = NULL;
Temp-> rchild = NULL;
Return temp;
}

Int main (int argc, char * argv []) {
Tree_node_t * root = createNode (10 );
Root-> lchild = createNode (12 );
Root-> rchild = createNode (15 );
Root-> lchild = createNode (25 );
Root-> lchild-> rchild = createNode (30 );
Root-> rchild-> lchild = createNode (36 );

Tree_node_t * head = changeToList (root );
PrintList (head );
Cin. get ();
Return 0;
}