Create an algorithm that asks the user for two positive numbers, call them “first” and “last”, and prints the sum of all the numbers between first [closed]

by

This doesn’t concern the code itself, but rather efficiency: This can easily be solved in constant time. Thanks to Gauss we know:

sum from 0 to N is: N * (N + 1) / 2

We can simply calculate the sum from first to last using that formula. Simply substract the sum from 0 to first – 1 from the sum from 0 to last:

int sum = last * (last + 1) / 2 - (first - 1) * (first) / 2;

Thanks to @MOehm for pointing out some mistakes in my answer.

More Related Contents:

  1. Insertion sort stops working after million input
  2. How to find out how many bits are set (equal 1) in the product of two integers [closed]
  3. C++ – Find numbers between first and last negative numbers in Array
  4. Program stopped working, when tried to run
  5. Absolute Distinct Numbers
  6. C++ throwing exception in recursive algorithm
  7. How to use Quick Sort to sort an array of strings
  8. How to get the maximum number after erasing n digits from the number [closed]
  9. Calculating pow(a,b) mod n
  10. Generating combinations in c++
  11. How to find which elements are in the bag, using Knapsack Algorithm [and not only the bag’s value]?
  12. Lock-free Progress Guarantees in a circular buffer queue
  13. Finding duplicates in O(n) time and O(1) space
  14. Getting the actual length of a UTF-8 encoded std::string?
  15. Fast String Hashing Algorithm with low collision rates with 32 bit integer [closed]
  16. Emulate “double” using 2 “float”s
  17. Algorithm for finding the smallest power of two that’s greater or equal to a given value [duplicate]
  18. How can I find the actual path found by BFS?
  19. Need for predictable random generator
  20. Splitting a string by a character
  21. How can I sort a std::map first by value, then by key?
  22. what is the difference between set and unordered_set in C++?
  23. Similar String algorithm
  24. Calculating the Amount of Combinations
  25. Better shading on BW display while rendering filled surfaces
  26. How can I sort an STL map by value?
  27. Algorithm to add or subtract days from a date?
  28. Creating N nested for-loops
  29. Mapping elements in 2D upper triangle and lower triangle to linear structure
  30. Fastest way to get the integer part of sqrt(n)?

Leave a Comment