In the name of God;
Testlib has nice random functions, here I want to suggest some other ones. The first and the second random functions are available in testlib, but the rest are not.
1, $$$\text{rnd.next(l, r)}$$$, it will return a random number in range $$$l$$$ to $$$r$$$ with equal weights :
2, $$$\text{rnd.wnext(l, r, w)}$$$, it will return a random number in range $$$l$$$ to $$$r$$$ with monotonically increasing/decreasing weights depending on $$$w$$$ :
If $$$w = 0$$$ then it will be equal to $$$\text{rnd.next(l, r)}$$$.
If $$$w > 0$$$ :
If $$$w < 0$$$ :
3, $$$\text{rnd.cnext(l, r, c)}$$$, it will return a random number in range $$$l$$$ to $$$r$$$ :
If $$$c = 0$$$ then it will be equal to $$$\text{rnd.next(l, r)}$$$
If $$$c > 0$$$ :
If $$$c < 0$$$, (I couldn't find a accurate graph for it) :
![ ](https://codeforces.net/fdb07d/cnext graph neg.png)
4, $$$\text{rnd.cwnext(l, r, c1, c2)}$$$, it will return a random number in range $$$l$$$ to $$$r$$$ like $$$\text{rnd.cnext{l, r, c}$$$, but its not centered around $$$\frac {r+l} 2$$$ :