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Leetcode – 78. Subsets

Given a set of distinct integers, nums, return all possible subsets (the power set). Note: The solution set must not contain duplicate subsets. Solution: Cascading Approach: Lets say, we have a set S={1,2,3,4}. Pick an element from set, ex. 4, now you have 2 sets - {[], [4]}. Now pick the second element from list ex. 3, now you … Continue reading Leetcode – 78. Subsets

Leetcode – 117. Populating Next Right Pointers in Each Node II

Given a binary tree struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL. Initially, all next pointers are set to NULL. Example: Input: {"\$id":"1","left":{"\$id":"2","left":{"\$id":"3","left":null,"next":null,"right":null,"val":4},"next":null,"right":{"\$id":"4","left":null,"next":null,"right":null,"val":5},"val":2},"next":null,"right":{"\$id":"5","left":null,"next":null,"right":{"\$id":"6","left":null,"next":null,"right":null,"val":7},"val":3},"val":1} Output: {"\$id":"1","left":{"\$id":"2","left":{"\$id":"3","left":null,"next":{"\$id":"4","left":null,"next":{"\$id":"5","left":null,"next":null,"right":null,"val":7},"right":null,"val":5},"right":null,"val":4},"next":{"\$id":"6","left":null,"next":null,"right":{"\$ref":"5"},"val":3},"right":{"\$ref":"4"},"val":2},"next":null,"right":{"\$ref":"6"},"val":1} Explanation: Given … Continue reading Leetcode – 117. Populating Next Right Pointers in Each Node II

Leetcode – 968 – Binary Tree Cameras

Given a binary tree, we install cameras on the nodes of the tree. Each camera at a node can monitor its parent, itself, and its immediate children. Calculate the minimum number of cameras needed to monitor all nodes of the tree. Example 1: Input: [0,0,null,0,0]Output: 1 Explanation: One camera is enough to monitor all nodes if placed as … Continue reading Leetcode – 968 – Binary Tree Cameras

Leetcode 99 – Recover Binary Search Tree – Constant space

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Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without changing its structure with constant space. Example 1: Input: [1,3,null,null,2]   1   / 3   \   2 Output: [3,1,null,null,2]   3   / 1   \   2 Example 2: Input: [3,1,4,null,null,2] 3 / \ 1 4 … Continue reading Leetcode 99 – Recover Binary Search Tree – Constant space