From 7be15ccb91d995d58f93faa0bd68b343b92f40a3 Mon Sep 17 00:00:00 2001
From: 0x40ba72637962bbeb3da5c36780ff8adea7e9cdfb <contact@tig.foundation>
Date: Tue, 23 Apr 2024 15:34:38 +0000
Subject: [PATCH] "Player 0x40ba72637962bbeb3da5c36780ff8adea7e9cdfb submitted
 'clarke_wright' for challenge vehicle_routing"

---
 .../src/vehicle_routing/clarke_wright.rs      | 87 +++++++++++++++++++
 tig-algorithms/src/vehicle_routing/mod.rs     |  2 +-
 2 files changed, 88 insertions(+), 1 deletion(-)
 create mode 100644 tig-algorithms/src/vehicle_routing/clarke_wright.rs

diff --git a/tig-algorithms/src/vehicle_routing/clarke_wright.rs b/tig-algorithms/src/vehicle_routing/clarke_wright.rs
new file mode 100644
index 00000000..ea192572
--- /dev/null
+++ b/tig-algorithms/src/vehicle_routing/clarke_wright.rs
@@ -0,0 +1,87 @@
+use tig_challenges::vehicle_routing::*;
+
+pub fn solve_challenge(challenge: &Challenge) -> anyhow::Result<Option<Solution>> {
+    let d = &challenge.distance_matrix;
+    let c = challenge.max_capacity;
+    let n = challenge.difficulty.num_nodes;
+
+    // Clarke-Wright heuristic for node pairs based on their distances to depot
+    // vs distance between each other
+    let mut scores: Vec<(i32, usize, usize)> = Vec::new();
+    for i in 1..n {
+        for j in (i + 1)..n {
+            scores.push((d[i][0] + d[0][j] - d[i][j], i, j));
+        }
+    }
+    scores.sort_by(|a, b| b.0.cmp(&a.0)); // Sort in descending order by score
+
+    // Create a route for every node
+    let mut routes: Vec<Option<Vec<usize>>> = (0..n).map(|i| Some(vec![i])).collect();
+    routes[0] = None;
+    let mut route_demands: Vec<i32> = challenge.demands.clone();
+
+    // Iterate through node pairs, starting from greatest score
+    for (s, i, j) in scores {
+        // Stop if score is negative
+        if s < 0 {
+            break;
+        }
+
+        // Skip if joining the nodes is not possible
+        if routes[i].is_none() || routes[j].is_none() {
+            continue;
+        }
+
+        let left_route = routes[i].as_ref().unwrap();
+        let right_route = routes[j].as_ref().unwrap();
+        let mut left_startnode = left_route[0];
+        let right_startnode = right_route[0];
+        let left_endnode = left_route[left_route.len() - 1];
+        let mut right_endnode = right_route[right_route.len() - 1];
+        let merged_demand = route_demands[left_startnode] + route_demands[right_startnode];
+
+        if left_startnode == right_startnode || merged_demand > c {
+            continue;
+        }
+
+        let mut left_route = routes[i].take().unwrap();
+        let mut right_route = routes[j].take().unwrap();
+        routes[left_startnode] = None;
+        routes[right_startnode] = None;
+        routes[left_endnode] = None;
+        routes[right_endnode] = None;
+
+        // reverse it
+        if left_startnode == i {
+            left_route.reverse();
+            left_startnode = left_endnode;
+        }
+        if right_endnode == j {
+            right_route.reverse();
+            right_endnode = right_startnode;
+        }
+
+        let mut new_route = left_route;
+        new_route.extend(right_route);
+
+        // Only the start and end nodes of routes are kept
+        routes[left_startnode] = Some(new_route.clone());
+        routes[right_endnode] = Some(new_route);
+        route_demands[left_startnode] = merged_demand;
+        route_demands[right_endnode] = merged_demand;
+    }
+
+    Ok(Some(Solution {
+        routes: routes
+            .into_iter()
+            .enumerate()
+            .filter(|(i, x)| x.as_ref().is_some_and(|x| x[0] == *i))
+            .map(|(_, mut x)| {
+                let mut route = vec![0];
+                route.append(x.as_mut().unwrap());
+                route.push(0);
+                route
+            })
+            .collect(),
+    }))
+}
diff --git a/tig-algorithms/src/vehicle_routing/mod.rs b/tig-algorithms/src/vehicle_routing/mod.rs
index 62bb1af6..08cc4a91 100644
--- a/tig-algorithms/src/vehicle_routing/mod.rs
+++ b/tig-algorithms/src/vehicle_routing/mod.rs
@@ -1,4 +1,4 @@
-// c002_a001 placeholder
+pub mod clarke_wright;
 // c002_a002 placeholder
 // c002_a003 placeholder
 // c002_a004 placeholder