Category leetcode

The original question can be found here. The question is asking to return all subsets of an integer array, and each element in the array is unique. Recursion Normally the question which is asking for all possible solutions are searching.…

The original question can be found here. The question is asking us to the minimum length of subarray that it’s sum is no less than target value. Brute Force The brute force we can immediately think of is to enumerate…

The original question can be found here. The question is asking us to find 2 numbers that their sum equals to target value, and exlictly, we cannot use data structures. So we cannot use hash table as in Leetcode 1:…

The original question can be found here. This question is asking to find the mimimum element in a rotated sorted array. But before tackling this question, I strongly suggest you to look at this question if you haven’t already. However,…

The original question can be found here. The question is asking us to check if target is in a rotated sorted array. Here the array can have duplicate numbers. Brute Force The brute force solution is scanning the whole array…

The original question can be found here. The question is asking us to find the target element in a 2-dimensional array. Each row is greater than the row above it. Within each row, elements are sorted as well. Brute Force…

The original question can be found here. The question is asking for a specific target value, if it exists in the array, return the index. Otherwise, return the index position that it should be inserted. Brute Force We just iterate…

The original question can be found here. It’s asking us to find an element that is grater than both left and right neighbors. Since it’s asking for a O(logn) solution, let’s directly jump to the binary search solution. There’re 4…

The original question can be found here. The question is asking us to find a target element in rotated sorted array. Since the question is explictly asking for a O(logn) solution, so let’s jump to the binary search solution. After…

The original question can be found here. The question is asking us to find the minimum element in a rotated sorted array. After analysing, we can observe the following: The array can be divided into 2 parts. The left part…

The original question can be found here. The question is asking us to return a peak element, which means, an element is greater than both 2 adjacent neighbors. Brute Force Scan the array: Time complexity: O(n). Space complexity: O(1). Binary…

The original question can be found here. The question is asking to return the k closet elements to target x. The array is sorted. Heap First solution is using a heap to keep track the current closest elements to x.…

The original question can be found here. The question is asking us to return the index of a target element, however, the size of the array is unknown. The only difference of this question from the traditional binary search question…

The original question can be found here. The question is asking to return a tuple with first and last position of target element in a sorted array. Brute Force Iterate through the whole array and keep track of first and…

The original question can be found here. The question is asking us to perform a binary search on an sorted array, which is a classical algorithm. If you haven’t, please visit my another post which detailed describe this algorithm. Time…

The original question can be found here. The question is asking to return the Nth fibonacci number. F(0) = 0, F(1) = 1 and F(n) = F(n – 1) + F(n – 2). The easist solution is using recursion. If…

The original question can be found here. It’s asking us to provide O(nlogn)solutions. Quick Sort The algorithm can be found here in my another post. Merge Sort The algorithm can be found here in my another post.

This is probably our very first coding preparation question. The original question can found here. This question is asking us to return the indices of 2 elements such that their sum equals to the target number. Brute Force The brute…

The original question can be found here. The question is asking if a string is palindromic if at most 1 character can be removed from string. Let’s look at an example: Let’s say we still use the 2 pointers apporach…

The original question can be found here. The question is asking for a given string, determine if it’s palindromic. Only alphanumeric letters are taking into account and letters’ cases are ignored. Reverse and Compare The first solution we can think…

The original question can be found here. There’re multiple solutions to this question, and we’ll start with the brute force one. Brute Force We enumerate all substrings and check if it’s palindromic. If yes, we update the final result by…

The original question can be found here. The question is asking to return the median number of 2 sorted arrays. Let’s say array nums1‘s length is m and nums2‘s length is n. If the sum of m and n is…

The original question can be found here. The question is aksing for the intersection of two arrays, and element in final result should be unique. There’re multiple solutions for this question. Hash Set Load one array into a hashset, and…

The original question can be found here. It’s asking us to merge array nums2 into array nums1. The most straightforward solution is: for each element inside array nums2, we insert into nums1 to find an appropriate position. Once we find…

The orignal question can be found here. The question is asking the number of subarrays which the sum value equals to K. The brute force solution is very straight forward. We simply enumerate all the possible subarrays to find out…

The original question can be found here. The question is aksing for the largest sum of the subarray. We can enumerate all possible subarrays and return the lagest sum. The time complexity is O(n^2)which is not quite acceptable. To find…

The original question can be found here. The question is asking to find the maximum number inside each sliding window(subarray). Brute Force Go through each subarray and find the maximum value. The time complexity is O(n*k), where n is the…

The original question can be found here. This question is quite tricky. I will say best of luck to you if this is the first time you see this question during a real interview. I’ll skip the brute force solution…