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Construct Tree from given Inorder and Preorder traversals

Let us consider the below traversals:

Inorder sequence: D B E A C

Preorder sequence: A B D E C

In a Preorder sequence! leftmost element is the root of the tree" #o we $now %A&

is root for given sequences" B' searching %A& in Inorder sequence! we can (nd out

all elements on left side of %A& are in left subtree and elements on right are in

right subtree" #o we $now below structure now"

A

) *

) *

D B E C

+e recursivel' follow above ste,s and get the following tree"

A

) *

) *

B C

) * )

) * )

D E

Algorithm: buildTree-.

/. Pic$ an element from Preorder" Increment a Preorder Inde0 1ariable -,reInde0

in below code. to ,ic$ ne0t element in ne0t recursive call"

2. Create a new tree node t3ode with the data as ,ic$ed element"

4. ind the ,ic$ed element&s inde0 in Inorder" Let the inde0 be inInde0"5. Call buildTree for elements before inInde0 and ma$e the built tree as left

subtree of t3ode"

6. Call buildTree for elements after inInde0 and ma$e the built tree as right

subtree of t3ode"

7. return t3ode"

Than$s to 8ohini and Tushar for suggesting the code"

C

9ava

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P'thon

) ,rogram to construct tree using inorder and ,reorder traversals )

;include

7/26/2019 Construct Tree From Given Inorder and Preorder Traversals

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return 3HLL?

) Pic$ current node from Preorder traversal using ,reInde0

and increment ,reInde0 )

struct node t3ode G new3ode-,re,reInde0.?

) If this node has no children then return )

if-in#trt GG inEnd.

return t3ode?

) Else (nd the inde0 of this node in Inorder traversal )

int inInde0 G search-in! in#trt! inEnd! t3ode=data.?

) Hsing inde0 in Inorder traversal! construct left and

right subtress )

t3ode=left G buildTree-in! ,re! in#trt! inInde0/.?

t3ode=right G buildTree-in! ,re! inInde0/! inEnd.?

return t3ode?

@

) HTILITJ H3CTIK3# )

) unction to (nd inde0 of value in arrstart"""end

The function assumes that value is ,resent in in )

int search-char arr! int strt! int end! char value.

>

int i?

for-i G strt? i

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>

if-arri GG value.

return i?

@

@

) el,er function that allocates a new node with the

given data and 3HLL left and right ,ointers" )

struct node new3ode-char data.

>

struct node node G -struct node.malloc-sieof-struct node..?

node=data G data?

node=left G 3HLL?

node=right G 3HLL?

return-node.?

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) This funtcion is here Must to test buildTree-. )

void ,rintInorder-struct node node.

>

if -node GG 3HLL.

return?

) (rst recur on left child )

,rintInorder-node=left.?

) then ,rint the data of node )

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,rintf-NOc N! node=data.?

) now recur on right child )

,rintInorder-node=right.?

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) Driver ,rogram to test above functions )

int main-.

>

char in G >FDF! FBF! FEF! FAF! FF! FCF@?

char ,re G >FAF! FBF! FDF! FEF! FCF! FF@?

int len G sieof-in.)sieof-in.?

struct node root G buildTree-in! ,re! ! len /.?

) Let us test the built tree b' ,rinting Insorder traversal )

,rintf-NInorder traversal of the constructed tree is *nN.?

,rintInorder-root.?

getchar-.?

@