# Construct Ancestor Matrix from a Given Binary Tree

Given a Binary Tree where all values are from 0 to n-1. Construct an ancestor matrix mat[n][n]. Ancestor matrix is defined as below.

```mat[i][j] = 1 if i is ancestor of j
mat[i][j] = 0, otherwise
```

Examples:

```Input: Root of below Binary Tree.
0
/   \
1     2
Output: 0 1 1
0 0 0
0 0 0

Input: Root of below Binary Tree.
5
/    \
1      2
/  \    /
0    4  3
Output: 0 0 0 0 0 0
1 0 0 0 1 0
0 0 0 1 0 0
0 0 0 0 0 0
0 0 0 0 0 0
1 1 1 1 1 0
```

We strongly recommend you to minimize your browser and try this yourself first.

Method 1

The idea is to traverse the tree. While traversing, keep track of ancestors in an array. When we visit a node, we add it to ancestor array and consider corresponding row in adjacency matrix. We mark all ancestors in its row as 1. Once a node and all its children are processed, we remove the node from ancestor array.

Below is the implementation of above idea.

## C++

 `// C++ program to construct ancestor matrix for ` `// given tree. ` `#include ` `using` `namespace` `std; ` `#define MAX 100 ` ` `  `/* A binary tree node */` `struct` `Node ` `{ ` `    ``int` `data; ` `    ``Node *left, *right; ` `}; ` ` `  `// Creating a global boolean matrix for simplicity ` `bool` `mat[MAX][MAX]; ` ` `  `// anc[] stores all ancestors of current node.  This ` `// function fills ancestors for all nodes. ` `// It also returns size of tree.  Size of tree is ` `// used to print ancestor matrix. ` `int` `ancestorMatrixRec(Node *root, vector<``int``> &anc) ` `{ ` `    ``/* base case */` `    ``if` `(root == NULL) ``return` `0;; ` ` `  `    ``// Update all ancestors of current node ` `    ``int` `data = root->data; ` `    ``for` `(``int` `i=0; ileft, anc); ` `    ``int` `r = ancestorMatrixRec(root->right, anc); ` ` `  `    ``// Remove data from list the list of ancestors ` `    ``// as all descendants of it are processed now. ` `    ``anc.pop_back(); ` ` `  `    ``return` `l+r+1; ` `} ` ` `  `// This function mainly calls ancestorMatrixRec() ` `void` `ancestorMatrix(Node *root) ` `{ ` `    ``// Create an empty ancestor array ` `    ``vector<``int``> anc; ` ` `  `    ``// Fill ancestor matrix and find size of ` `    ``// tree. ` `    ``int` `n = ancestorMatrixRec(root, anc); ` ` `  `    ``// Print the filled values ` `    ``for` `(``int` `i=0; idata = data; ` `    ``node->left = node->right = NULL; ` `    ``return` `(node); ` `} ` ` `  `/* Driver program to test above functions*/` `int` `main() ` `{ ` `    ``/* Construct the following binary tree ` `                ``5 ` `              ``/   \ ` `            ``1      2 ` `          ``/  \    / ` `         ``0    4  3    */` `    ``Node *root        = newnode(5); ` `    ``root->left        = newnode(1); ` `    ``root->right       = newnode(2); ` `    ``root->left->left  = newnode(0); ` `    ``root->left->right = newnode(4); ` `    ``root->right->left = newnode(3); ` ` `  `    ``ancestorMatrix(root); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java Program to construct ancestor matrix for a given tree ` `import` `java.util.*; ` ` `  `class` `GFG ` `{ ` `    ``// ancestorMatrix function to populate the matrix of ` `    ``public` `static` `void` `ancestorMatrix(Node root ,  ` `                                    ``int` `matrix[][],``int` `size) ` `    ``{ ` `         `  `        ``// base case: ` `        ``if` `(root==``null``) ` `        ``return` `; ` `         `  `        ``// call recursively for a preorder {left} ` `        ``ancestorMatrix(root.left, matrix, size); ` `         `  `        ``// call recursively for preorder {right} ` `        ``ancestorMatrix(root.right, matrix, size); ` `         `  `        ``// here we will reach the root node automatically ` `        ``// try solving on pen and paper ` `         `  `        ``if` `(root.left != ``null``) ` `        ``{ ` `            ``// make the current node as parent of its children node ` `            ``matrix[root.data][root.left.data] = ``1``; ` `             `  `            ``// iterate through all the columns of children node  ` `            ``// all nodes which are children to ` `            ``// children of root node will also  ` `            ``// be children of root node ` `            ``for` `(``int` `i = ``0``; i < size; i++) ` `            ``{ ` `                ``// if children of root node is a parent  ` `                ``// of someone (i.e 1) then make that node  ` `                ``// as children of root also ` `                ``if` `(matrix[root.left.data][i] == ``1``) ` `                ``matrix[root.data][i] = ``1``; ` `            ``} ` `        ``} ` `         `  `        ``// same procedure followed for right node as well  ` `        ``if` `(root.right != ``null``) ` `        ``{ ` `            ``matrix[root.data][root.right.data] = ``1``; ` `             `  `            ``for` `(``int` `i = ``0``; i < size; i++) ` `            ``{ ` `                ``if` `(matrix[root.right.data][i]==``1``) ` `                ``matrix[root.data][i] = ``1``; ` `            ``} ` `        ``} ` `             `  `         `  `    ``} ` `     `  `    ``// Driver program to test the program ` `    ``public` `static` `void` `main(String[] args)  ` `    ``{ ` `         `  `        ``// construct the binary tree as follows ` `        ``Node tree_root = ``new` `Node(``5``); ` `        ``tree_root.left = ``new` `Node (``1``); ` `        ``tree_root.right = ``new` `Node(``2``); ` `        ``tree_root.left.left = ``new` `Node(``0``); ` `        ``tree_root.left.right = ``new` `Node(``4``); ` `        ``tree_root.right.left = ``new` `Node(``3``); ` `         `  `        ``// size of matrix  ` `        ``int` `size = ``6``; ` `        ``int` `matrix [][] = ``new` `int``[size][size]; ` `         `  `        ``ancestorMatrix(tree_root, matrix, size); ` `         `  `        ``for` `(``int` `i = ``0``; i < size; i++) ` `        ``{ ` `            ``for` `(``int` `j = ``0``; j < size; j++) ` `            ``{ ` `                ``System.out.print(matrix[i][j]+``" "``); ` `            ``} ` `            ``System.out.println(); ` `        ``} ` `    ``} ` `     `  `    ``// node class for tree node ` `    ``static` `class` `Node  ` `    ``{ ` `        ``public` `int` `data ; ` `        ``public` `Node left ,right; ` `        ``public` `Node (``int` `data) ` `        ``{ ` `            ``this``.data = data; ` `            ``this``.left = ``this``.right = ``null``; ` `        ``} ` `    ``} ` `} ` ` `  `// This code is contributed by Sparsh Singhal `

## Python3

 `# Python3 program to construct ancestor  ` `# matrix for given tree. ` ` `  `class` `newnode: ` `    ``def` `__init__(``self``, data): ` `        ``self``.data ``=` `data ` `        ``self``.left ``=` `self``.right ``=` `None` `         `  `# anc[] stores all ancestors of current node.  ` `# This function fills ancestors for all nodes.  ` `# It also returns size of tree. Size of tree   ` `# is used to print ancestor matrix.  ` `def` `ancestorMatrixRec(root, anc): ` `    ``global` `mat, ``MAX` `     `  `    ``# base case  ` `    ``if` `root ``=``=` `None``: ` `        ``return` `0` ` `  `    ``# Update all ancestors of current node  ` `    ``data ``=` `root.data ` `    ``for` `i ``in` `range``(``len``(anc)): ` `        ``mat[anc[i]][data] ``=` `1` ` `  `    ``# Push data to list of ancestors  ` `    ``anc.append(data)  ` ` `  `    ``# Traverse left and right subtrees  ` `    ``l ``=` `ancestorMatrixRec(root.left, anc)  ` `    ``r ``=` `ancestorMatrixRec(root.right, anc)  ` ` `  `    ``# Remove data from list the list of ancestors  ` `    ``# as all descendants of it are processed now.  ` `    ``anc.pop(``-``1``)  ` ` `  `    ``return` `l ``+` `r ``+` `1` ` `  `# This function mainly calls ancestorMatrixRec()  ` `def` `ancestorMatrix(root): ` `     `  `    ``# Create an empty ancestor array  ` `    ``anc ``=` `[] ` ` `  `    ``# Fill ancestor matrix and find  ` `    ``# size of tree.  ` `    ``n ``=` `ancestorMatrixRec(root, anc)  ` ` `  `    ``# Print the filled values ` `    ``for` `i ``in` `range``(n): ` `        ``for` `j ``in` `range``(n): ` `            ``print``(mat[i][j], end ``=` `" "``)  ` `        ``print``() ` ` `  `# Driver Code ` `MAX` `=` `100` `mat ``=` `[[``0``] ``*` `MAX` `for` `i ``in` `range``(``MAX``)] ` ` `  `# Construct the following binary tree  ` `#         5  ` `#         / \  ` `#     1     2  ` `#     / \ /  ` `#     0 4 3  ` `root ``=` `newnode(``5``)  ` `root.left ``=` `newnode(``1``)  ` `root.right ``=` `newnode(``2``)  ` `root.left.left ``=` `newnode(``0``)  ` `root.left.right ``=` `newnode(``4``)  ` `root.right.left ``=` `newnode(``3``)  ` ` `  `ancestorMatrix(root) ` ` `  `# This code is contributed by PranchalK  `

## C#

 `// C# Program to construct ancestor matrix for a given tree  ` `using` `System; ` ` `  `class` `GFG  ` `{ ` `    ``// ancestorMatrix function to populate the matrix of  ` `    ``public` `static` `void` `ancestorMatrix(Node root, ` `                        ``int` `[,]matrix, ``int` `size)  ` `    ``{ ` ` `  `        ``// base case:  ` `        ``if` `(root == ``null``)  ` `        ``{ ` `            ``return``; ` `        ``} ` ` `  `        ``// call recursively for a preorder {left}  ` `        ``ancestorMatrix(root.left, matrix, size); ` ` `  `        ``// call recursively for preorder {right}  ` `        ``ancestorMatrix(root.right, matrix, size); ` ` `  `        ``// here we will reach the root node automatically  ` `        ``// try solving on pen and paper  ` `        ``if` `(root.left != ``null``) ` `        ``{ ` `            ``// make the current node as parent of its children node  ` `            ``matrix[root.data,root.left.data] = 1; ` ` `  `            ``// iterate through all the columns of children node  ` `            ``// all nodes which are children to  ` `            ``// children of root node will also  ` `            ``// be children of root node  ` `            ``for` `(``int` `i = 0; i < size; i++)  ` `            ``{ ` `                ``// if children of root node is a parent  ` `                ``// of someone (i.e 1) then make that node  ` `                ``// as children of root also  ` `                ``if` `(matrix[root.left.data,i] == 1)  ` `                ``{ ` `                    ``matrix[root.data,i] = 1; ` `                ``} ` `            ``} ` `        ``} ` ` `  `        ``// same procedure followed for right node as well  ` `        ``if` `(root.right != ``null``) ` `        ``{ ` `            ``matrix[root.data,root.right.data] = 1; ` ` `  `            ``for` `(``int` `i = 0; i < size; i++)  ` `            ``{ ` `                ``if` `(matrix[root.right.data,i] == 1)  ` `                ``{ ` `                    ``matrix[root.data,i] = 1; ` `                ``} ` `            ``} ` `        ``} ` ` `  `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `Main(String[] args) ` `    ``{ ` ` `  `        ``// construct the binary tree as follows  ` `        ``Node tree_root = ``new` `Node(5); ` `        ``tree_root.left = ``new` `Node(1); ` `        ``tree_root.right = ``new` `Node(2); ` `        ``tree_root.left.left = ``new` `Node(0); ` `        ``tree_root.left.right = ``new` `Node(4); ` `        ``tree_root.right.left = ``new` `Node(3); ` ` `  `        ``// size of matrix  ` `        ``int` `size = 6; ` `        ``int` `[,]matrix = ``new` `int``[size,size]; ` ` `  `        ``ancestorMatrix(tree_root, matrix, size); ` ` `  `        ``for` `(``int` `i = 0; i < size; i++)  ` `        ``{ ` `            ``for` `(``int` `j = 0; j < size; j++)  ` `            ``{ ` `                ``Console.Write(matrix[i,j] + ``" "``); ` `            ``} ` `            ``Console.WriteLine(); ` `        ``} ` `    ``} ` ` `  `    ``// node class for tree node  ` `    ``public` `class` `Node ` `    ``{ ` ` `  `        ``public` `int` `data; ` `        ``public` `Node left, right; ` ` `  `        ``public` `Node(``int` `data)  ` `        ``{ ` `            ``this``.data = data; ` `            ``this``.left = ``this``.right = ``null``; ` `        ``} ` `    ``} ` `}  ` ` `  `// This code is contributed by 29AjayKumar  `

Output:

```0 0 0 0 0 0
1 0 0 0 1 0
0 0 0 1 0 0
0 0 0 0 0 0
0 0 0 0 0 0
1 1 1 1 1 0
```

Time complexity of above solution is O(n2).

Method 2

This method doesn’t use any auxiliary space to store values in the vector. Create a 2D matrix( say M) of the given size. Now the idea is to traverse the tree in PreOrder. While traversing, keep track of the last ancestor.
When we visit a node, if the node is NULL return, else assign M[lastAncestorValue][currentNodeValue]=1.
Through this, we have the Matrix(M) which keeps tracks of the Lowest Ancestor, Now by applying transitive closure to this Matrix(M), we get the required result.

Below is the implementation of the above idea.

## C++

 `// C++ program to construct ancestor matrix for  ` `// given tree.  ` `#include  ` `using` `namespace` `std;  ` `#define size 6  ` ` `  `int` `M[size][size]={0}; ` ` `  `/* A binary tree node */` `struct` `Node  ` `{  ` `    ``int` `data;  ` `    ``Node *left, *right;  ` `};  ` ` `  `/* Helper function to create a new node */` `Node* newnode(``int` `data)  ` `{  ` `    ``Node* node = ``new` `Node;  ` `    ``node->data = data;  ` `    ``node->left = node->right = NULL;  ` `    ``return` `(node);  ` `}  ` ` `  `void` `printMatrix(){ ` `        ``for``(``int` `i=0;idata; ` `             `  `        ``//Since there is no ancestor for root node, ` `        ``// so we doesn't assign it's value as 1             ` `        ``if``(index==-1)index=root->data; ` `        ``else`  `M[index][preData]=1;     ` `     `  `    ``MatrixUtil(root->left,preData); ` `    ``MatrixUtil(root->right,preData); ` `} ` ` `  `void` `Matrix(Node *root){ ` `    ``// Call Func MatrixUtil ` `    ``MatrixUtil(root,-1); ` `     `  `     `  `    ``//Applying Transitive Closure for the given Matrix ` `    ``for``(``int` `i=0;ileft     = newnode(1);  ` `    ``root->right     = newnode(2);  ` `    ``root->left->left = newnode(0);  ` `    ``root->left->right = newnode(4);  ` `    ``root->right->left = newnode(3);  ` ` `  `    ``Matrix(root);  ` `     `  ` `  `    ``return` `0;  ` `}  `

Output:

```0 0 0 0 0 0
1 0 0 0 1 0
0 0 0 1 0 0
0 0 0 0 0 0
0 0 0 0 0 0
1 1 1 1 1 0
```

How to do reverse – construct tree from ancestor matrix?
Construct tree from ancestor matrix

Don’t stop now and take your learning to the next level. Learn all the important concepts of Data Structures and Algorithms with the help of the most trusted course: DSA Self Paced. Become industry ready at a student-friendly price.

My Personal Notes arrow_drop_up

Article Tags :
Practice Tags :

3

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.