golf z func

[lrvideckis]

The idea behind this change is:

each iteration of the while loop will increase the right border  
$r$  of the match segment

https://cp-algorithms.com/string/z-function.html#asymptotic-behavior-of-the-algorithm

So basically if we successfully enter in the while loop, then we know the condition (i + z[i] > r) is true

here's an AC to show it's still O(n) https://codeforces.com/contest/126/submission/216604260

[lrvideckis]

btw, the same idea can be used here

https://github.com/kth-competitive-programming/kactl/blob/main/content/strings/Manacher.h#L19-L20

[bjorn-martinsson]

On the subject on codegolfing the z function. You can save one more character by changing

z[i] = i >= r ? 0 : min(r - i, z[i - l]);

into

z[i] = i > r ? 0 : min(r - i, z[i - l]);

This works since z is non-negative, so removing the = doesn't make any difference.

[lrvideckis]

https://judge.yosupo.jp/submission/153328

https://cses.fi/paste/c38edc2216ec6a0165ec83/ for https://cses.fi/problemset/task/1733/

[IvanRenison]

@lrvideckis I tested this version o Zfunc and the current one, and in the problem in witch I tested it it was faster with the current one than with this one. Did you made a more exhaustive test about speed? (I only tested it in one problem, so it may not be something general)

[bjorn-martinsson]

@lrvideckis I tested this version o Zfunc and the current one, and in the problem in witch I tested it it was faster with the current one than with this one. Did you made a more exhaustive test about speed? (I only tested it in one problem, so it may not be something general)

Could you link to your submissions comparing the two?

[IvanRenison]

Could you link to your submissions comparing the two?

Current versión: https://codeforces.com/gym/105053/submission/254710440
Your versión: https://codeforces.com/gym/105053/submission/254709569

Files in github:
Current versión: https://github.com/IvanRenison/ProgrammingProblems/blob/e73f34d3d818d37ea0c341e976578f70cc5e89b3/ICPC%20contests/Latin%20American%20Super-Regional%202024/H.cpp
Your versión: https://github.com/IvanRenison/ProgrammingProblems/blob/152993eb7982d2585833ff5d574654601bd6a69e/ICPC%20contests/Latin%20American%20Super-Regional%202024/H.cpp