dsa1 min read
Find the Duplicate Number — Binary Search on Count
Find the duplicate in array of n+1 integers in [1,n] using binary search on value with count-of-smaller logic.
Read →
Counting
7 articles
dsa2 min read
Island Perimeter — Grid Edge Counting
Calculate the perimeter of an island in a binary grid. Each land cell contributes 4 edges minus 2 for each land neighbour.
Read →
dsa2 min read
Count Bad Pairs — Complement Counting with HashMap
Count pairs (i,j) where j-i != nums[j]-nums[i] by counting good pairs via frequency map of nums[i]-i.
Read →
dsa2 min read
Tuple with Same Product — Product Frequency Map
Count tuples (a,b,c,d) where a*b=c*d by counting pairs with each product using a frequency map.
Read →
dsa4 min read
Inclusion-Exclusion Principle: Counting with Overlaps
Apply the inclusion-exclusion principle to count elements satisfying union of conditions. Solves divisibility, coverage, and derangement problems.
Read →
dsa2 min read
Number of Ways to Arrive at Destination — Dijkstra + Count
Count the number of shortest paths from source to destination using modified Dijkstra that tracks both minimum distance and path count simultaneously.
Read →
dsa1 min read
Count Distinct Substrings — Suffix Array + LCP
Count the number of distinct substrings using the suffix array and LCP array. Total substrings minus sum of LCP values gives distinct count in O(n log n).
Read →