**Objective:** **– **Given a inorder and level order traversal, construct a binary tree from that.

**Input:** Inorder and level order traversal

**Approach:**

int[] inOrder = { 4, 2, 5, 1, 6, 3, 7 };int[] levelOrder = { 1, 2, 3, 4, 5, 6, 7 };

- First element in the
will be the*levelorder []**root*of the tree, here it is 1. - Now the search element 1 in
say you find it at position*inorder[]*,*i*, once you find it, make note of elements which are left to*i*(this will construct the) and elements which are right to**leftsubtree***i*( this will construct the).**rightSubtree** - Suppose in previous step, there are X number of elements which are left of ‘
*i’*(which will construct the leftsubtree), but these X elements will not be in the consecutive in levelorder[] so we will extract these elements fromby maintaining their sequence and store it in an array say*levelorder[]*.*newLeftLevel[]* - Similarly if there are Y number of elements which are right of ‘i’ (which will construct the rightsubtree), but these Y elements will not be in the consecutive in levelorder[] so we will extract these elements from
by maintaining their sequence and store it in an array say*levelorder[]**newRightLevel[]*. - From previous two steps construct the left and right subtree and link it to root.left and root.right respectively by making recursive calls using
and*newLeftLevel[]***newRightLevel[]**. - See the picture for better explanation.

**Complete Code:**

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public class InorderLevelOrderToTree { | |

public Node makeBTree(int[] inorder, int[] levelOrder, int iStart, int iEnd) { | |

if (iStart > iEnd) { | |

return null; | |

} | |

int rootVal = levelOrder[0]; | |

Node root = new Node(rootVal); | |

if (iStart == iEnd) { | |

return root; | |

} | |

int index = findIndex(inorder, rootVal, iStart, iEnd); | |

int[] newleftLevel = newLevelOrder(inorder, levelOrder, iStart, | |

index – 1); | |

int[] newrighttLevel = newLevelOrder(inorder, levelOrder, index + 1, | |

iEnd); | |

root.left = makeBTree(inorder, newleftLevel, iStart, index – 1); | |

root.right = makeBTree(inorder, newrighttLevel, index + 1, iEnd); | |

return root; | |

} | |

public int[] newLevelOrder(int[] inorder, int[] levelOrder, int iStart, | |

int iEnd) { | |

int[] newlevel = new int[iEnd – iStart + 1]; | |

int x = 0; | |

for (int i = 0; i < levelOrder.length; i++) { | |

if (findIndex(inorder, levelOrder[i], iStart, iEnd) != –1) { | |

newlevel[x] = levelOrder[i]; | |

x++; | |

} | |

} | |

return newlevel; | |

} | |

public int findIndex(int[] inorder, int value, int iStart, int iEnd) { | |

int x = –1; | |

for (int i = iStart; i <= iEnd; i++) { | |

if (value == inorder[i]) { | |

x = i; | |

} | |

} | |

return x; | |

} | |

public void printINORDER(Node root) { | |

if (root != null) { | |

printINORDER(root.left); | |

System.out.print(" " + root.data); | |

printINORDER(root.right); | |

} | |

} | |

public static void main(String args[]) { | |

int[] inOrder = { 4, 2, 5, 1, 6, 3, 7 }; | |

int[] levelOrder = { 1, 2, 3, 4, 5, 6, 7 }; | |

InorderLevelOrderToTree i = new InorderLevelOrderToTree(); | |

Node x = i.makeBTree(inOrder, levelOrder, 0, inOrder.length – 1); | |

System.out.println("inorder traversal of constructed tree : "); | |

i.printINORDER(x); | |

} | |

} | |

class Node { | |

int data; | |

Node left; | |

Node right; | |

public Node(int data) { | |

this.data = data; | |

left = null; | |

right = null; | |

} | |

} |

**Output**:

inorder traversal of constructed tree : 4 2 5 1 6 3 7