dsa1 min read
Count of Range Sum — Merge Sort / BIT
Count subarray sums within [lower, upper]. Use prefix sums and merge sort: during merge count pairs of prefix sums with difference in range.
Read →
All Posts
1575 articles
dsa1 min read
Number of Longest Increasing Subsequences — DP + BIT
Count all LIS of maximum length. DP: track length and count. Segment tree on values enables O(n log n) solution.
Read →
dsa1 min read
Shifting Letters II — Difference Array
Apply range shift operations to letters. Difference array: mark +1 at start and -1 at end+1, prefix sum gives net shift at each position.
Read →
dsa1 min read
Range Sum Query 2D Immutable — 2D Prefix Sum
Sum of rectangle region. Precompute 2D prefix sums: prefix[i][j] = sum of all cells from (0,0) to (i-1,j-1). Inclusion-exclusion for query.
Read →
dsa1 min read
My Calendar III — Difference Array / Seg Tree
Track maximum booking overlaps at any time. Difference array: +1 at start, -1 at end; running max of prefix sum. Lazy segment tree for dynamic range.
Read →
Page 146 of 315