From 321e4353d8d9a447c472bc5f0d3acbfcf0309bae Mon Sep 17 00:00:00 2001
From: Fredrik Robertsen <fredrikr79@pm.me>
Date: Fri, 6 Feb 2026 09:22:52 +0100
Subject: [PATCH] add elitism

---
 src/common.odin |  3 ++-
 src/ga.odin     | 41 ++++++++++++++++++++++++++++++++++++++++-
 src/main.odin   |  4 ++--
 3 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/src/common.odin b/src/common.odin
index 3381a6d..c12f5c8 100644
--- a/src/common.odin
+++ b/src/common.odin
@@ -9,9 +9,10 @@ POPULATION_SIZE :: 100
 GENERATIONS :: 100
 TOURNAMENT_SIZE :: 3
 CROSSOVER_RATE :: 0.8
-MUTATION_RATE :: 0.01
+MUTATION_RATE :: 0.05
 RANDOM_SEED :: u64(42)
 OUTPUT_FILE :: "output/data.csv"
+ELITISM_COUNT :: 2
 
 Problem :: struct {
 	name:            string,
diff --git a/src/ga.odin b/src/ga.odin
index 8da4b18..7fc05a9 100644
--- a/src/ga.odin
+++ b/src/ga.odin
@@ -135,10 +135,25 @@ bit_flip_mutation :: proc(chrom: Chromosome) {
 	}
 }
 
+clone_chromosome :: proc(chrom: Chromosome) -> Chromosome {
+    size := bit_array.len(chrom)
+    clone := bit_array.create(size)
+    for i in 0 ..< size {
+        bit_array.set(clone, i, bit_array.get(chrom, i))
+    }
+    return clone
+}
+
 create_offspring :: proc(pop: ^Population, fitnesses: []f64, maximize: bool) -> Population {
 	offspring: Population
 
-	for i := 0; i < POPULATION_SIZE; i += 2 {
+	elite_idx := get_best_indices(fitnesses[:], ELITISM_COUNT, maximize)
+	defer delete(elite_idx)
+	for i in 0 ..< ELITISM_COUNT {
+		offspring[i] = clone_chromosome(pop[elite_idx[i]])
+	}
+
+	for i := ELITISM_COUNT; i < POPULATION_SIZE; i += 2 {
 		parent1 := tournament_selection(pop, fitnesses, maximize)
 		parent2 := tournament_selection(pop, fitnesses, maximize)
 
@@ -158,6 +173,30 @@ create_offspring :: proc(pop: ^Population, fitnesses: []f64, maximize: bool) ->
 	return offspring
 }
 
+get_best_indices :: proc(fitnesses: []f64, count: int, maximize: bool) -> []int {
+    indices := make([]int, len(fitnesses))
+    for i in 0 ..< len(indices) {
+        indices[i] = i
+    }
+
+    // Partial sort for top N
+    for i in 0 ..< count {
+        best := i
+        for j in i + 1 ..< len(indices) {
+            is_better := maximize ? fitnesses[indices[j]] > fitnesses[indices[best]] : fitnesses[indices[j]] < fitnesses[indices[best]]
+            if is_better {
+                best = j
+            }
+        }
+        indices[i], indices[best] = indices[best], indices[i]
+    }
+
+    result := make([]int, count)
+    copy(result, indices[:count])
+    delete(indices)
+    return result
+}
+
 write_results :: proc(filename: string, stats: []Stats) -> bool {
 	handle, err := os.open(filename, os.O_CREATE | os.O_WRONLY | os.O_TRUNC, 0o644)
 	if err != os.ERROR_NONE {return false}
diff --git a/src/main.odin b/src/main.odin
index 017ea5d..5dc7010 100644
--- a/src/main.odin
+++ b/src/main.odin
@@ -8,8 +8,8 @@ main :: proc() {
 	// Choose problem
 	problem_type := "feature_selection" // or "knapsack"
 
-	state := rand.create(RANDOM_SEED)
-	context.random_generator = runtime.default_random_generator(&state)
+	// state := rand.create(RANDOM_SEED)
+	// context.random_generator = runtime.default_random_generator(&state)
 
 	problem: Problem
 	switch problem_type {