NTPC Interview Questions and Answers

Find all pairs of elements in an array that add up to a given target.

• Iterate through the array and store each element in a hashmap along with its index.

• For each element, check if the target minus the element exists in the hashmap.

• If found, print the pair of elements. If not found, print (-1, -1).

Find the minimum number of arrows needed to burst all balloons by shooting arrows from left to right.

• Sort the array in ascending order to make it easier to determine the minimum number of arrows needed.

• Iterate through the sorted array and count the number of times the height decreases.

• The count of height decreases plus 1 gives the minimum number of arrows needed to burst all balloons.

Validate if a binary tree is a Binary Search Tree (BST) based on given properties.

• Check if the left subtree of a node contains only nodes with data less than the node's data.

• Verify if the right subtree of a node contains only nodes with data greater than the node's data.

• Ensure that both the left and right subtrees are also binary search trees.

• Iterate through the tree in level order form to validate the BST properties.

Construct a binary tree from preorder traversal and leaf node information.

• Create a binary tree using preorder traversal and leaf node information

• Use recursion to build the tree

• Handle both leaf and non-leaf nodes appropriately

Given a binary tree, print all root-to-leaf paths in order.

• Traverse the binary tree from root to leaf nodes, keeping track of the path nodes.

• Use depth-first search (DFS) to explore all possible paths.

• Return each path as a string of nodes separated by spaces.

• Handle cases where nodes have NULL values by skipping them in the path.

• Ensure the order of nodes in each path is maintained.

Identify all distinct triplets within an array that sum up to a specified number.

• Iterate through the array and use nested loops to find all possible triplets.

• Check if the sum of the triplet equals the specified number.

• Print the valid triplets or return -1 if no triplet exists.