Classic Problems

Non-Overlapping Segments

Number of Sets of K Non-Overlapping Line Segments

Reverse Pairs

Examples:

• Count of Smaller Numbers After Self
• Reverse Pairs
• Number of Pairs Satisfying Inequality

Solutions:

• Merge Sort
• Fenwick Tree
• Segment Tree
• Binary Search Tree

Swim in Rising Water

• Swim in Rising Water

Solutions:

• Dijkstra’s Algorithm
• BinarySearch + BFS/DFS
• Union-Find

Subarray Sum Equals K

Count Number of Nice Subarrays

• Sliding window
• If we apply nums[i] -> nums[i] % 2, the problem becomes Subarray Sum Equals K, and we can use hash map to store the count of each sum during iteration.