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43 articles
The classic stock problem asked at Amazon, Google and Microsoft. Learn the O(n) greedy "min so far" approach with complete solutions in C, C++, Java, JavaScript and Python, plus extensions to Stock II, III and IV.
Move all zeroes to end while maintaining relative order of non-zero elements. Optimal O(n) two-pointer solution with minimal writes. Full C, C++, Java, JavaScript and Python code.
Merge two sorted arrays in-place by filling from the end. The classic 3-pointer technique asked at Meta and Microsoft. Full solutions in C, C++, Java, JavaScript and Python.
Remove duplicates from a sorted array in-place using the write pointer pattern. O(n) time, O(1) space. Full solutions in C, C++, Java, JavaScript, Python with follow-up for allowing k duplicates.
Return the third distinct maximum or the max if fewer than 3 distinct values exist. Three-variable tracking O(n) O(1) solution.
Rotate array right by k steps. Triple reverse trick: reverse whole, reverse first k, reverse rest. O(n) time O(1) space.
Find the minimum element in a rotated sorted array with no duplicates. Binary search: the minimum is in the unsorted half. O(log n) time O(1) space.
Find the lexicographically next permutation in-place using a two-pass scan from the right.
Sort an array of 0s, 1s, and 2s in-place in one pass using Dijkstra's Dutch National Flag algorithm.
Generate all permutations of distinct integers using in-place swap backtracking.
Find the smallest contiguous subarray with sum >= target using the shrinkable sliding window technique.
Search for a word in a 2D grid using DFS backtracking with in-place visited marking.
Find minimum number of jumps to reach the last index using greedy BFS-style level tracking.
Find the missing number in [0..n] using the Gauss sum formula or XOR in O(n) time O(1) space.
Calculate trapped rain water using inward two pointers that track left-max and right-max, replacing the classic O(n) space approach.
Find the maximum in every sliding window of size k in O(n) using a monotonic decreasing deque.
Find the smallest missing positive integer in O(n) time O(1) space using in-place cyclic sort to place each number at its correct index.
Find the largest rectangle in a histogram in O(n) using a monotonic increasing stack that computes area when a shorter bar is encountered.
Find the median of two sorted arrays in O(log(min(m,n))) by binary searching for the correct partition point.
Find the largest rectangle of 1s in a binary matrix by treating each row as a histogram and applying the Largest Rectangle in Histogram algorithm.
Find two indices that add to target in O(n) by storing each number in a HashMap and looking up the complement.
Check if two strings are anagrams by comparing their character frequency counts using an array or HashMap.
Determine if a number is happy by repeatedly summing digit squares and detecting cycles using a HashSet or Floyd algorithm.
Group strings that are anagrams together by using their sorted form as a HashMap key.
Find the k most frequent elements in O(n) using bucket sort by frequency instead of a heap.
Design a Least Recently Used cache with O(1) get and put operations using a HashMap combined with a doubly linked list.
Check if a string is a palindrome after removing non-alphanumeric characters using inward two pointers.
Reverse an array of characters in-place using the classic two-pointer swap technique.
Remove duplicates in-place from a sorted array using a write pointer that only advances on unique elements.
Merge two sorted arrays in-place from the end to avoid overwriting elements using three pointers.
Find the maximum number of consecutive 1s achievable by flipping at most k zeros, using a variable sliding window.
Find the longest substring without duplicate characters using a HashSet-backed shrinkable sliding window.
Find the longest substring with at most k character replacements by tracking the maximum frequency char in the window.
Check if any permutation of s1 is a substring of s2 using a fixed-size sliding window with character frequency comparison.
Maximize water trapped between two vertical lines using inward two pointers that always move the shorter line inward.
Find all unique triplets summing to zero by sorting and using two pointers for each fixed element with careful duplicate skipping.
Find two numbers summing to target in a 1-indexed sorted array using inward two pointers in O(n) time O(1) space.
Find k closest integers to x in a sorted array using binary search to locate the optimal left boundary of the window.
Find the maximum consecutive ones in a binary array when you can flip at most k zeros, identical to the Max Consecutive Ones III pattern.
Find the smallest window in s containing all characters of t using a have/need counter to track when the window is valid.
Find the maximum in every sliding window of size k in O(n) using a monotonic decreasing deque of indices.
Sort an array of 0s, 1s, and 2s in one pass using the Dutch National Flag 3-pointer algorithm.
Calculate trapped rainwater using optimal two-pointer approach that tracks left and right maximums without extra space.