How do I print an integer in binary with leading zeros?

I'm doing some bit twiddling and I'd like to print all the bits in my u16.

let flags = 0b0000000000101100u16;
println!("flags: {:#b}", flags);

This prints flags: 0b101100.

How do I make it print flags: 0b0000000000101100?

I have come to prefer these patterns:

println!("{:08b}", 1i8);
println!("{:016b}", 12000u16);
println!("{:032b}", 624485u32);

it will print:

00000001
0010111011100000
00000000000010011000011101100101

Stack Overflow Q#44690439, score: 9