UVa 264 - Count on Cantor

Summary
No point in brute forcing this thing 10^7 will take a long time :)

Explanation

 * We can generalize this pattern in order to figure out the fraction.
 * Try to sum up all the numbers sequentially until you have figured out the range in which your number will belong.
 * Once we establish the range, you can simply figure out the distance from the current position and finish off the problem.
 * Follow this general algorithm. Pre-compute an array of summations 4500 in length.  Binary search to find exactly what diagonal in the matrix would be referenced.  Next, note the when to add/subtract from the numerator and denominators.  Easy solution from there.

fzort: This problem also has a O(1) solution. It's easy to compute the index d of the diagonal a given number n is in. The number of elements before diagonal d is

$$n=\frac{d(d + 1)}{2}$$

, so the number n is in diagonal

$$d=\left \lfloor \frac{1 + \sqrt{1+8n}}{2} \right \rfloor$$

Input
1 3 14 7 10000000

Output
TERM 1 IS 1/1 TERM 3 IS 2/1 TERM 14 IS 2/4 TERM 7 IS 1/4 TERM 10000000 IS 2844/1629

Solutions

 * Code All the Problems