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mmghannam merged 1 commit into from
Jan 29, 2025
Merged

Add knapsack example #205

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77 changes: 77 additions & 0 deletions examples/knapsack.rs
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Original file line number Diff line number Diff line change
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use russcip::minimal_model;
use russcip::prelude::*;

#[derive(Debug)]
struct Knapsack {
sizes: Vec<usize>,
values: Vec<usize>,
capacity: usize,
}

#[derive(Debug)]
struct KnapsackSolution {
items: Vec<usize>,
value: f64,
}

impl Knapsack {
fn new(sizes: Vec<usize>, values: Vec<usize>, capacity: usize) -> Self {
assert_eq!(
sizes.len(),
values.len(),
"Sizes and values must have the same length"
);
Knapsack {
sizes,
values,
capacity,
}
}

/// Solves the 0-1 knapsack as an integer program
fn solve(&self) -> KnapsackSolution {
let mut model = minimal_model().maximize();

let vars: Vec<_> = self
.values
.iter()
.map(|&value| model.add(var().binary().obj(value as f64)))
.collect();

let var_sizes = vars
.iter()
.zip(self.sizes.iter())
.map(|(var, &size)| (var, size as f64));
model.add(cons().le(self.capacity as f64).expr(var_sizes));

let solved_model = model.solve();

let sol = solved_model.best_sol().unwrap();
let items: Vec<_> = vars
.iter()
.enumerate()
.filter(|(_, v)| sol.val(v) > 1e-6)
.map(|(i, _)| i)
.collect();
let value = sol.obj_val();

KnapsackSolution { items, value }
}
}

fn main() {
let knapsack = Knapsack::new(vec![2, 3, 4, 5], vec![3, 4, 5, 6], 6);
let solution = knapsack.solve();

println!("Input: {:?}", knapsack);
println!("Solution items: {:?}", solution.items);
println!(
"Value: {} = {:?}",
solution.value,
solution
.items
.iter()
.map(|&i| (knapsack.sizes[i], knapsack.values[i]))
.collect::<Vec<_>>()
);
}
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