From c02d5ca0ab3973c8704895fd6536ae649f2ac485 Mon Sep 17 00:00:00 2001
From: Anders Olsson <anders.e.olsson@gmail.com>
Date: Fri, 24 Apr 2026 08:58:09 +0200
Subject: [PATCH] perf(game): replace order.clone()+position() with inverse
 permutation

---
 src/game.rs | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/game.rs b/src/game.rs
index 131fb82..e45d676 100644
--- a/src/game.rs
+++ b/src/game.rs
@@ -192,15 +192,19 @@ impl<'a, D: Drift> Game<'a, D> {
             .map(|si| lhood_win[si] * lhood_lose[si])
             .collect();
 
-        // Map sorted-team likelihoods back to original team order.
-        let order = arena.sort_buf.clone();
+        // Inverse permutation: inv[orig_i] = sorted_i (O(n), avoids clone + O(n²) search).
+        let mut inv = vec![0usize; n_teams];
+        for (si, &orig_i) in arena.sort_buf.iter().enumerate() {
+            inv[orig_i] = si;
+        }
+
         self.likelihoods = self
             .teams
             .iter()
             .zip(self.weights.iter())
             .enumerate()
             .map(|(orig_i, (players, weights))| {
-                let sorted_i = order.iter().position(|&x| x == orig_i).unwrap();
+                let sorted_i = inv[orig_i];
                 let m = m_t_ft[sorted_i];
                 let performance = players
                     .iter()