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MST of a digraph??

if the root of the spanning tree is given, how to get the MST of a digraph?


Independent geometric random variables

X and Y are independent geometric random variables, e.e. P(X=k)=P(Y=k)=(1-p)
p^k,
k=0,1,...
U=min(X,Y), V=max{X,Y}, W=V-U

P(W=j)=?

Tags: statistics

Three pieces of pizzas

Three pieces of pizzas, 1 with both sides burned, 1 with 1 side burned, 1 with 0 side burned. Stack them together blindly, you see the top surface is burned, ...


Lion and Man

A lion and a Christian in a closed circular Roman arena have equal maximum speeds. Assume the lion starts at the center and the man is at the boundary circle. ...

Tags: puzzle

Counting 1s

Consider a function which, for a given whole number n, returns the number of 1s required when writing out all numbers between 0 and n.

For example, f(13)=6. Notice ...

Tags: google number