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When working with two digit strings, we sometimes need to remove characters to make them identical while minimizing the sum of deleted digits. This problem can be solved using dynamic programming with a variation of the Longest Common Subsequence (LCS) algorithm. Given two strings s and t containing only digits, we need to remove digits from both strings so that the remaining strings are identical, and the sum of deleted digits is minimized. Example If the input is s = "41272" and t = "172", we can remove "4" and "2" from the first string to get ... Read More
Given two strings s and t, we need to find the length of the minimum substring in s that contains all characters of t. If no such substring exists, we return -1. This is known as the Minimum Window Substring problem. For example, if s = "thegrumpywizardmakes" and t = "wake", the shortest substring containing all characters of "wake" is "wizardmake" with length 10. Algorithm We use the sliding window technique with two pointers ? Create a frequency counter for characters in string t Use two pointers (start and end) to maintain a sliding window ... Read More
A palindrome is a string that reads the same forwards and backwards. To transform a string into a palindrome using minimum adjacent swaps, we need to check if it's possible and then calculate the swaps required. For a string to form a palindrome, at most one character can have an odd frequency (which would be the middle character in odd-length palindromes). Algorithm The solution involves two steps: Check if palindrome formation is possible by counting character frequencies Use two pointers to match characters from both ends, swapping adjacent elements when needed Example ... Read More
Given a list of numbers, two numbers nums[i] and nums[j] are considered adjacent when there is no number with a value between them in the original list. We need to find the minimum possible difference of indices |j - i| such that nums[j] and nums[i] are adjacent. For example, if the input is nums = [1, -9, 6, -6, 2], the output will be 2, as we can see that 2 and 6 are adjacent elements (no value between 2 and 6 exists in the list) and they are 2 indices apart. Algorithm Approach To solve this ... Read More
Suppose we have a 4 x 4 board of letters and a list of words, we have to find the largest number of words that can be generated in the board by a sequence of adjacent letters, using one cell at most once per word (but we can reuse cells for other words). We can go up, down, left, right, or diagonal direction. Problem Example If the input is like ? ... Read More
Suppose we have a list of non-overlapping intervals sorted by end time. We need to merge a target interval into this list while maintaining the non-overlapping and sorted properties. For example, if we have intervals = [[1, 15], [25, 35], [75, 90]] and target = [10, 30], the output will be [[1, 35], [75, 90]] because the target interval [10, 30] overlaps with both [1, 15] and [25, 35], merging them into a single interval [1, 35]. Algorithm To solve this problem, we follow these steps: Add the target interval to the list of intervals ... Read More
Suppose we have a list of numbers nums and a list of queries where each query contains [x, limit]. We have to find a list such that for each query [x, limit], we find an element e in nums such that e ≤ limit and e XOR x is maximized. If there is no such element, return -1. Problem Understanding For example, if nums = [3, 5, 9] and queries = [[4, 6], [2, 0]], then the output will be [3, -1]. For the first query, we can use 3 or 5 from nums (both ≤ 6). 3 ... Read More
Suppose we have a string s and another string t, where t is a subsequence of s. We need to find the maximum length of a substring that can be removed from s such that t remains a subsequence of the remaining string. So, if the input is like s = "xyzxyxz" and t = "yz", then the output will be 4, as we can remove a substring of length 4 while keeping "yz" as a subsequence. Approach The algorithm works by considering three scenarios ? Remove a suffix after matching all characters of t ... Read More
We need to split a list of numbers into k contiguous groups and find the maximum possible value of the smallest group's sum. This is a classic binary search optimization problem. For example, given nums = [2, 6, 4, 5, 8] and k = 3, we can split into groups [2, 6], [4, 5], [8] with sums 8, 9, 8. The smallest sum is 8, which is our answer. Algorithm Approach We use binary search on the answer space. For each potential minimum sum, we check if it's possible to split the array into exactly k groups ... Read More
Suppose we have a binary string s and two values zero_one and one_zero. We can delete any substring "01" and receive zero_one points, or remove any substring "10" and receive one_zero points. We need to find the maximum number of points we can get after any number of operations. So, if the input is like s = "10100101", zero_one = 3, one_zero = 2, then the output will be 11. We can remove "01" three times to get 3×3 = 9 points. Then the remaining string is "10". By removing this we get another 2 points, so the total ... Read More