Problems
November 28, 2022
Binary tree vertical order traversal
We will use BFS to traverse the tree. We will keep track of the horizontal distance of each node from the root. We will use a dictionary to store the nodes at each horizontal distance. We will use a...
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Count pairs in two arrays
nums1[i] + nums1[j] > nums2[i] + nums2[j], i < j can be converted to (nums1[i]-nums2[i]) + (nums1[j]-nums2[j]) > 0, i < j.
At this point, we will realize that...
November 28, 2022
Find players with zero or one losses
We use 3 different hashset to store zero losses, one loss and more than one loss. Then we iterate through the results array and update the hashsets accordingly. Finally, we iterate...
November 28, 2022
Remove zero sum consecutive nodes from linked list
We will keep track of the prefix sum of the linked list. If the prefix sum is repeated, we will remove the nodes between the repeated prefix sum and the current prefix sum. Time complexity:...
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Minimize product sum of two arrays
We will sort the two arrays, first one in ascending order and second one in descending order. That will make sure the product of both array's item will be minimized. Then we will iterate over the...
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Validate binary tree nodes
We will first find the root of the tree. Then we will traverse the tree and check if we can reach all the nodes from the root. We will use BFS to traverse. If we can reach all the nodes, then the...
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Design hashset
We will use a boolean array to store the values. We will use the value as the index of the array and set the value to true if the value is added and false if the value is...
November 27, 2022
Binary tree upside down
We will use recursive DFS to solve the problem. We will recursively call the function on the left child of the root. Then we will set the left child of the root to the right child of the root. Then...
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Arithmetic slices II subsequence
We will use dynamic programming to solve the problem. We will use a hashmap to store the number of arithmetic slices that ends with the current number. We will iterate over the numbers, and for each...
ReadNovember 27, 2022
Arithmetic slices
We will take a top-down approach to solve the problem. Then we memoize each subproblem to avoid duplicate computation.
Time complexity: O(n), n is the length of nums
Space...