Two pointers, sliding window, fast and slow pointers, binary search variants, backtracking, monotonic stacks and bit manipulation tricks.
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- Two-pointer technique definition
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Use two pointers starting from different positions to solve array or list problems in O(n) time- When is two-pointer approach useful?
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When finding pairs, removing elements, or comparing values in a sorted array in a single pass- How do pointers move in a sorted array two-pointer problem?
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If sum is too large, move right pointer left; if too small, move left pointer right- What does convergence mean in two-pointer?
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The left and right pointers move toward each other until they meet- Two-pointer example: find pair with target sum
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Place left pointer at start, right at end; move them based on whether current sum is less than or greater than target- How to handle duplicates in two-pointer approach?
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Skip duplicate values by advancing pointer past all equal elements- Time complexity advantage of two-pointer
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Reduces time from O(n^2) brute force to O(n) with only one or two passes through data- Reverse array in place with two pointers
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Start pointers at both ends, swap elements, move toward center until they meet- Sliding window technique definition
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Maintain a window of consecutive elements that expands and contracts based on a condition- When to use sliding window?
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For subarray or substring problems where you need to find minimum, maximum, or optimal window matching a condition- Expand-contract pattern in sliding window
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Expand window by moving right pointer until condition breaks, then contract by moving left pointer to restore condition- Common sliding window problems
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Longest substring without repeating, minimum window substring, maximum sum subarray of fixed size- Data structure for tracking sliding window state
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Hash map to track character frequency or set to track distinct elements in current window- Time complexity of sliding window
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O(n) because each element is visited at most twice, once by right pointer and once by left pointer- Find longest substring without repeating characters
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Use sliding window with hash map tracking last seen index; move left pointer when duplicate found
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