Given an array, nums, there is a sliding window of size k which is moving from the very left of the array to the very right. Both courses 1 and 2 should be taken after you finished course 0. I see everything in one place. It sounds a lot like a binary search problem. four sum. I faced this issue early in the term when I didn’t know what I didn’t know, which is a particularly pernicious problem. We can detect if it contains any cycles and compute a topological sort in the same pass. DEV Community © 2016 - 2020. Sorting is not a problem-solving technique per see but as you have seen in the previous sections we have been able to solve many problems by either sorting the input or assuming it was sorted and then applying one of the other techniques. Just use my solution in case you get stuck. Possible follow-up questions to ask the interviewer. Given an integer n, return all distinct solutions to the n-queens puzzle. A well-understood problem is already a half-solved problem. By design, the element at the front of our dequeue will contain the maximum of the sliding window, which is what we are interested in. Here you have a couple of problems that can be easily solved after sorting the input. I find it more fun and you can add them to your Github profile. This is one of the most common variations of the two-pointer technique: introducing an offset so that one of the pointers reaches a certain condition, the other one is in the position you are interested in. This problem can be solved just by using the XOR operator: If we XOR all the numbers in the array (integers in the range [0,n]) with all the integers in [0 to n], the pairs will produce zeroes and the missing number will be XORed with 0 (resulting in itself), solving our problem. As soon as you see a matrix, think of a graph. Design your own circular dequeue, to fully grasp the internals of this data structure. Each node will contain: Knowing what problem a data structure is trying to solve and breaking it down to its basic elements makes it much easier to implement it and especially to remember what the data structure is about and when it can be used. The tree directory follows the spatial decomposition of the quadtree. This list is part of the study notes that I took before I applied to Amazon. For every index i, you need to generate two solutions: Here’s a simple implementation of what we have discussed. And a problem can be solved with many approaches, ultimately we look into the pros… Think for a minute how this can be achieved with two pointers moving at different speeds. This will be extremely slow for large values of N. Since the attraction between two particles decays with the square of the distance, we can neglect the contribution of particles that are far. You may assume all four edges of the grid are all surrounded by water. Based on the recipe I described above, you will need: For more practice, you can try the following problems: There might be simpler solutions but focus on using this technique to get a better grasp of it. Your answer should be sorted by frequency from highest to lowest. If you want to learn more about this data structure, I recommend these two to see a quadtree in action. To take course 1 you should have finished course 0. ] This problem (and its variations) is very straightforward: To sink the island, you need to visit all the surrounding 1s in the matrix, which is equivalent to visit all the neighbors of that node and of all its neighbors, which sounds a lot like a recursive problem. To represent a cycle in the given linked list, we use an integer pos which represents the position (0-indexed) in the linked list where the tail connects to. As I mentioned, this is a very powerful approach that you should always keep in mind. So one correct course order is [0,1,2,3]. [1,3], We're a place where coders share, stay up-to-date and grow their careers. It is up to you. Great article! Return the index of the first occurrence of needle in a haystack, or -1 if the needle is not part of the haystack. "..Q."]. Here's my solution in C++. If the size is not known, this can be done instead: Write a program to solve a Sudoku puzzle by filling the empty cells. This might not be the simplest way of solving this problem, but it is a clear application of a trie. You will learn much more from it than from reading my solution without trying first. This is a very common technique: transform a problem whose solution you don't know to a problem that you can solve.

## problem solving techniques in data structure

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