Challenge Given a positive integer \$n\$, count the number of \$n\times n\$ binary matrices (i.e. whose entries are \$0\$ or \$1\$) with exactly two \$1\$'s in each rows and two \$1\$'s in each column. Here are a few examples of valid matrices for \$n=4\$: 1100 1100 1100 110...

An addition-subtraction chain, is a sequence \$a_1, a_2, a_3, ... ,a_n\$, such that \$a_1=1\$ and for all \$i > 1\$, there exist \$j,k<i\$ such that \$a_i = a_j \pm a_k\$. Your task, is given a number \$x\$, find the shortest addition-subtraction chain, such that \$a_n = x\$. Rules You can assum...

I'm proposing we create a minecraft tag for challenges relating to the game Minecraft. There are currently 15 applicable questions: this, this, and this just to name a few.