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Find parent of each node in a tree for multiple queries
• Last Updated : 30 Jan, 2020

Given a tree with N vertices numbered from 0 to N – 1 and Q query containing nodes in the tree, the task is to find the parent node of the given node for multiple queries. Consider the 0th node as the root node and take the parent of the root node as the root itself.

Examples:

```Tree:
0
/  \
1    2
|   / \
3  4   5

Input: N = 2
Output: 0
Explanation:
Parent of node 2 is node 0 i.e root node

Input: N = 3
Output: 1
Explanation:
Parent of node 3 is node 1
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:
By default, we assign the parent of the root node as the root itself. Then, we traverse the tree using Breadth First Traversal(BFS). When we mark the children of node s as visited, we also assign the parent node of these children as the node s. Finally, for different queries, the value of the parent[] of the node is printed.

Below is the implementation of above approach:

## C++

 `// C++ implementation for ` `// the above approach ` ` `  `#include ` `using` `namespace` `std; ` ` `  `const` `int` `sz = 1e5; ` ` `  `// Adjacency list representation ` `// of the tree ` `vector<``int``> tree[sz + 1]; ` ` `  `// Boolean array to mark all the ` `// vertices which are visited ` `bool` `vis[sz + 1]; ` ` `  `// Array of vector where ith index ` `// stores the path from the root ` `// node to the ith node ` `int` `ans[sz + 1]; ` ` `  `// Function to create an ` `// edge between two vertices ` `void` `addEdge(``int` `a, ``int` `b) ` `{ ` ` `  `    ``// Add a to b's list ` `    ``tree[a].push_back(b); ` ` `  `    ``// Add b to a's list ` `    ``tree[b].push_back(a); ` `} ` ` `  `// Modified Breadth-First Function ` `void` `bfs(``int` `node) ` `{ ` ` `  `    ``// Create a queue of {child, parent} ` `    ``queue > qu; ` ` `  `    ``// Push root node in the front of ` `    ``qu.push({ node, 0 }); ` ` `  `    ``while` `(!qu.empty()) { ` `        ``pair<``int``, ``int``> p = qu.front(); ` ` `  `        ``// Dequeue a vertex from queue ` `        ``qu.pop(); ` `        ``ans[p.first] = p.second; ` `        ``vis[p.first] = ``true``; ` ` `  `        ``// Get all adjacent vertices of the dequeued ` `        ``// vertex s. If any adjacent has not ` `        ``// been visited then enqueue it ` `        ``for` `(``int` `child : tree[p.first]) { ` `            ``if` `(!vis[child]) { ` `                ``qu.push({ child, p.first }); ` `            ``} ` `        ``} ` `    ``} ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` ` `  `    ``// Number of vertices ` `    ``int` `n = 6; ` ` `  `    ``addEdge(0, 1); ` `    ``addEdge(0, 2); ` `    ``addEdge(1, 3); ` `    ``addEdge(2, 4); ` `    ``addEdge(2, 5); ` ` `  `    ``// Calling modified bfs function ` `    ``bfs(0); ` ` `  `    ``int` `q[] = { 2, 3 }; ` ` `  `    ``for` `(``int` `i = 0; i < 2; i++) { ` `        ``cout << ans[q[i]] << ``'\n'``; ` `    ``} ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation for ` `// the above approach ` `import` `java.util.*; ` ` `  `class` `GFG  ` `{ ` `static` `int` `sz = (``int``) 1e5; ` ` `  `// Adjacency list representation ` `// of the tree ` `static` `Vector []tree = ``new` `Vector[sz + ``1``]; ` ` `  `// Boolean array to mark all the ` `// vertices which are visited ` `static` `boolean` `[]vis = ``new` `boolean``[sz + ``1``]; ` ` `  `// Array of vector where ith index ` `// stores the path from the root ` `// node to the ith node ` `static` `int` `[]ans = ``new` `int``[sz + ``1``]; ` `static` `class` `pair ` `{  ` `    ``int` `first, second;  ` `    ``public` `pair(``int` `first, ``int` `second)  ` `    ``{  ` `        ``this``.first = first;  ` `        ``this``.second = second;  ` `    ``}  ` `}  ` ` `  `// Function to create an ` `// edge between two vertices ` `static` `void` `addEdge(``int` `a, ``int` `b) ` `{ ` ` `  `    ``// Add a to b's list ` `    ``tree[a].add(b); ` ` `  `    ``// Add b to a's list ` `    ``tree[b].add(a); ` `} ` ` `  `// Modified Breadth-First Function ` `static` `void` `bfs(``int` `node) ` `{ ` ` `  `    ``// Create a queue of {child, parent} ` `    ``Queue qu = ``new` `LinkedList<>(); ` ` `  `    ``// Push root node in the front of ` `    ``qu.add(``new` `pair(node, ``0` `)); ` ` `  `    ``while` `(!qu.isEmpty())  ` `    ``{ ` `        ``pair p = qu.peek(); ` ` `  `        ``// Dequeue a vertex from queue ` `        ``qu.remove(); ` `        ``ans[p.first] = p.second; ` `        ``vis[p.first] = ``true``; ` ` `  `        ``// Get all adjacent vertices of the dequeued ` `        ``// vertex s. If any adjacent has not ` `        ``// been visited then enqueue it ` `        ``for` `(``int` `child : tree[p.first])  ` `        ``{ ` `            ``if` `(!vis[child]) ` `            ``{ ` `                ``qu.add(``new` `pair(child, p.first )); ` `            ``} ` `        ``} ` `    ``} ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String[] args)  ` `{ ` `     `  `    ``// Number of vertices ` `    ``int` `n = ``6``; ` `    ``for` `(``int` `i = ``0``; i < sz + ``1``; i++)  ` `        ``tree[i] = ``new` `Vector(); ` `         `  `    ``addEdge(``0``, ``1``); ` `    ``addEdge(``0``, ``2``); ` `    ``addEdge(``1``, ``3``); ` `    ``addEdge(``2``, ``4``); ` `    ``addEdge(``2``, ``5``); ` ` `  `    ``// Calling modified bfs function ` `    ``bfs(``0``); ` ` `  `    ``int` `q[] = { ``2``, ``3` `}; ` ` `  `    ``for` `(``int` `i = ``0``; i < ``2``; i++) ` `    ``{ ` `        ``System.out.println(ans[q[i]]); ` `    ``} ` `} ` `} ` ` `  `// This code is contributed by 29AjayKumar `

## Python

 `# Python implementation for  ` `# the above approach  ` ` `  `sz ``=` `10``*``*``5` ` `  `# Adjacency list representation  ` `# of the tree  ` `tree ``=` `[[] ``for` `_ ``in` `range``(sz ``+` `1``)] ` ` `  `# Boolean array to mark all the  ` `# vertices which are visited  ` `vis ``=` `[``0``] ``*` `(sz ``+` `1``) ` ` `  `# Array of vector where ith index  ` `# stores the path from the root  ` `# node to the ith node  ` `ans ``=` `[``0``] ``*` `(sz ``+` `1``) ` ` `  `# Function to create an  ` `# edge between two vertices  ` `def` `addEdge(a, b): ` `     `  `    ``# Add a to b's list  ` `    ``tree[a].append(b)  ` `     `  `    ``# Add b to a's list  ` `    ``tree[b].append(a)  ` ` `  `# Modified Breadth-First Function  ` `def` `bfs(node): ` `     `  `    ``# Create a queue of child, parent  ` `    ``qu ``=` `[] ` `     `  `    ``# Push root node in the front of  ` `    ``qu.append([node, ``0``])  ` `     `  `    ``while` `(``len``(qu)): ` `        ``p ``=` `qu[``0``] ` `         `  `        ``# Dequeue a vertex from queue  ` `        ``qu.pop(``0``) ` `        ``ans[p[``0``]] ``=` `p[``1``]  ` `        ``vis[p[``0``]] ``=` `True` `         `  `        ``# Get all adjacent vertices of the dequeued  ` `        ``# vertex s. If any adjacent has not  ` `        ``# been visited then enqueue it  ` `        ``for` `child ``in` `tree[p[``0``]]: ` `            ``if` `(``not` `vis[child]): ` `                ``qu.append([child, p[``0``]])  ` `                 `  `# Driver code  ` ` `  `# Number of vertices  ` `n ``=` `6` ` `  `addEdge(``0``, ``1``)  ` `addEdge(``0``, ``2``)  ` `addEdge(``1``, ``3``)  ` `addEdge(``2``, ``4``)  ` `addEdge(``2``, ``5``)  ` ` `  `# Calling modified bfs function  ` `bfs(``0``)  ` ` `  `q ``=` `[``2``, ``3``] ` ` `  `for` `i ``in` `range``(``2``): ` `    ``print``(ans[q[i]])  ` ` `  `# This code is contributed by SHUBHAMSINGH10 `

## C#

 `// C# implementation of the approach ` `using` `System; ` `using` `System.Collections.Generic; ` ` `  `class` `GFG  ` `{ ` `static` `int` `sz = (``int``) 1e5; ` ` `  `// Adjacency list representation ` `// of the tree ` `static` `List<``int``> []tree = ``new` `List<``int``>[sz + 1]; ` ` `  `// Boolean array to mark all the ` `// vertices which are visited ` `static` `Boolean []vis = ``new` `Boolean[sz + 1]; ` ` `  `// Array of vector where ith index ` `// stores the path from the root ` `// node to the ith node ` `static` `int` `[]ans = ``new` `int``[sz + 1]; ` `public` `class` `pair ` `{  ` `    ``public` `int` `first, second;  ` `    ``public` `pair(``int` `first, ``int` `second)  ` `    ``{  ` `        ``this``.first = first;  ` `        ``this``.second = second;  ` `    ``}  ` `}  ` ` `  `// Function to create an ` `// edge between two vertices ` `static` `void` `addEdge(``int` `a, ``int` `b) ` `{ ` ` `  `    ``// Add a to b's list ` `    ``tree[a].Add(b); ` ` `  `    ``// Add b to a's list ` `    ``tree[b].Add(a); ` `} ` ` `  `// Modified Breadth-First Function ` `static` `void` `bfs(``int` `node) ` `{ ` ` `  `    ``// Create a queue of {child, parent} ` `    ``Queue qu = ``new` `Queue(); ` ` `  `    ``// Push root node in the front of ` `    ``qu.Enqueue(``new` `pair(node, 0 )); ` ` `  `    ``while` `(qu.Count != 0)  ` `    ``{ ` `        ``pair p = qu.Peek(); ` ` `  `        ``// Dequeue a vertex from queue ` `        ``qu.Dequeue(); ` `        ``ans[p.first] = p.second; ` `        ``vis[p.first] = ``true``; ` ` `  `        ``// Get all adjacent vertices of the dequeued ` `        ``// vertex s. If any adjacent has not ` `        ``// been visited then enqueue it ` `        ``foreach` `(``int` `child ``in` `tree[p.first])  ` `        ``{ ` `            ``if` `(!vis[child]) ` `            ``{ ` `                ``qu.Enqueue(``new` `pair(child, p.first )); ` `            ``} ` `        ``} ` `    ``} ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main(String[] args)  ` `{ ` `     `  `    ``// Number of vertices ` `    ``for` `(``int` `i = 0; i < sz + 1; i++)  ` `        ``tree[i] = ``new` `List<``int``>(); ` `         `  `    ``addEdge(0, 1); ` `    ``addEdge(0, 2); ` `    ``addEdge(1, 3); ` `    ``addEdge(2, 4); ` `    ``addEdge(2, 5); ` ` `  `    ``// Calling modified bfs function ` `    ``bfs(0); ` ` `  `    ``int` `[]q = { 2, 3 }; ` ` `  `    ``for` `(``int` `i = 0; i < 2; i++) ` `    ``{ ` `        ``Console.WriteLine(ans[q[i]]); ` `    ``} ` `} ` `} ` ` `  `// This code is contributed by 29AjayKumar `

Output:

```0
1
```

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