Max value

Grains
Grains in Rust 
pub fn total() -> u64 {
    u64::MAX
}

The maximum value for an unsigned integer gives the total number of grains on all sixty-four squares. It is essentially getting all of the bits of a 64-bit number set to 1.

This might seem like a "cheat". To understand how it works, consider just two squares that are represented in bits as 00.

  • If there is a grain on square One, then the first bit (on the right) is set to binary 01, which is the decimal value of 1.
  • If there are two grains on square Two, then the second bit (from the right) is set to binary 10, which is the decimal value of 2.
  • If there are is one grain on Square One and two grains on square Two, then both bits are set to binary 11, which is the decimal value of 3.
  • So, with all of the two bits set you get 3, which is the number of all grains on both squares.

Getting the value of u64::MAX is getting 64 bits set to 1, which is just what we need to get the total number of grains on sixty-four squares, given that the grains double on each square, starting with one grain on the first square.

23rd Apr 2025 · Found it useful?

Other Approaches to Grains in Rust

Other ways our community solved this exercise
pub fn square(s: u32) -> u64 {
    // code snipped
    2u64.pow(s - 1)
}

pub fn total() -> u64 {
    (2_u128.pow(64) - 1) as u64
}
pow

Use pow to raise 2 by a specified power. 

pub fn square(s: u32) -> u64 {
    // code snipped
    1 << (s - 1)
}

pub fn total() -> u64 {
    ((1_u128 << 64) - 1) as u64
}
Bit-shifting

Use bit-shifting to raise 2 by a specified power.