README.md

Competetive-Code-Learns

This repo includes the code that I must remember at all times when I encounter a problem

1. Large Array can be declared globally
2. Copy by reference + Global Declarations reduces running time
3. Avoid endl, it increases runnning time. https://stackoverflow.com/questions/213907/stdendl-vs-n
4. Bitsets may be highly useful in reducing complexities
   Example: https://www.hackerearth.com/practice/algorithms/graphs/graph-representation/practice-problems/algorithm/utkarsh-in-gardens-february-easy/description/
5. Custom Lowerbound Function :https://stackoverflow.com/questions/12968498/compare-function-in-lower-bound
6. Distinct Elements in range l to r using BIT: https://www.geeksforgeeks.org/queries-number-distinct-elements-subarray/
   
7. Important DPs:
   • https://www.hackerearth.com/practice/algorithms/dynamic-programming/introduction-to-dynamic-programming-1/practice-problems/algorithm/number-of-rs-1/
     How to detect the application of Maximum Subarray Problem:For a range from 1 to n, at some point i we check ans=max(maxSubArraySum(1...i),maxSubArraySum(i+1...n),maxSumPassingThroughi) which is seen in divide and conquer equivalent of Maximum Subarray Problem
     
     
   • Partion such that two subsets have minimum difference: https://www.hackerearth.com/practice/algorithms/dynamic-programming/introduction-to-dynamic-programming-1/practice-problems/algorithm/amazing-test/
     
     
   • https://www.codechef.com/problems/SPAR3
     
     
   • Important 3d dp: https://www.hackerearth.com/practice/algorithms/dynamic-programming/2-dimensional/practice-problems/algorithm/shift-the-array-4074fac2/description/
     Approrach the question using 26^n and then see how to memoize
     
     
   • Algorithm for finding minimum cycle length in unweighted graph(use bfs and approach below for unweighted undirected graph ) - Complexity O(e^2) [So far minimum complexity for finding min cycle length I have seen] https://www.geeksforgeeks.org/find-minimum-weight-cycle-undirected-graph/
   • Gray Codes differ by one bit in each successive step
     
     
   • https://www.quora.com/q/competitiveprogramming2/Cut-Vertex-Articulation-point
     
     
   • Method to generate subsets of a a number in binary->
     Let the number be x and tmp = x, then we can successively compute tmp=(tmp-1)&x, tmp will be the subset -> stop at 0
     Example let x = 13, and thus tmp = 13, now :
     ->First Subset : 13
     ->Second Subbset : (13-1)&13 = 12
     ->Third Subset: (12-1)&13 = 9
     ->Fourth Subset: (9-1)&13 = 8
     ->Fifth Subset: (8-1)&13 = 5
     ->Sixth Subset: (5-1)%13 = 4
     ->Seventh Subset: (4-1)%13 = 1
     ->Eighth Subset: (1-0)&13 = 0
     Reference: Inner loop of suboptimal solution section on https://codeforces.com/blog/entry/45223