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use num_traits::Num; use std::iter::FusedIterator; pub struct Partitions<T: Num + PartialOrd + Copy> { n: T, m: T, } impl<T: Num + PartialOrd + Copy> Partitions<T> { pub fn new(n: T, m: T) -> Self { assert!(n >= m); Self { n, m } } } impl<T: Num + PartialOrd + Copy> Iterator for Partitions<T> { type Item = T; #[inline] fn next(&mut self) -> Option<Self::Item> { if self.n.is_zero() { return None; } let v = self.n / self.m; self.n = self.n - v; self.m = self.m - T::one(); Some(v) } } impl ExactSizeIterator for Partitions<usize> { #[inline] fn len(&self) -> usize { self.m } } impl<T: Num + PartialOrd + Copy> FusedIterator for Partitions<T> {} #[cfg(test)] mod tests { use super::Partitions; #[test] fn case_1() { let iter = Partitions::new(10, 3); assert_eq!(iter.len(), 3); assert_eq!(iter.sum::<usize>(), 10); } #[test] fn case_1_next() { let mut iter = Partitions::new(10, 3); assert_eq!(iter.next(), Some(3)); assert_eq!(iter.next(), Some(3)); assert_eq!(iter.next(), Some(4)); } #[test] fn case_2() { let iter = Partitions::new(123, 14); assert_eq!(iter.len(), 14); assert_eq!(iter.sum::<usize>(), 123usize); } #[test] fn case_3() { let iter = Partitions::new(739845, 192873); assert_eq!(iter.len(), 192873); assert_eq!(iter.sum::<usize>(), 739845usize); } #[test] fn case_4() { let iter = Partitions::<f64>::new(10.0, 3.0); assert_eq!(iter.sum::<f64>(), 10.0); } fn between(v: f64, min: f64, max: f64) -> bool { min <= v && v <= max } #[test] fn case_4_next() { let mut iter = Partitions::<f64>::new(10.0, 3.0); assert!(between(iter.next().unwrap(), 3.33, 3.34)); assert!(between(iter.next().unwrap(), 3.33, 3.34)); assert!(between(iter.next().unwrap(), 3.33, 3.34)); } }