Initial data commit

Task/Evolutionary-algorithm/PHP/evolutionary-algorithm.php

@@ -0,0 +1,45 @@
+define('TARGET','METHINKS IT IS LIKE A WEASEL');
+define('TBL','ABCDEFGHIJKLMNOPQRSTUVWXYZ ');
+
+define('MUTATE',15);
+define('COPIES',30);
+define('TARGET_COUNT',strlen(TARGET));
+define('TBL_COUNT',strlen(TBL));
+
+// Determine number of different chars between a and b
+
+function unfitness($a,$b)
+{
+        $sum=0;
+        for($i=0;$i<strlen($a);$i++)
+                if($a[$i]!=$b[$i]) $sum++;
+        return($sum);
+}
+
+function mutate($a)
+{
+        $tbl=TBL;
+        for($i=0;$i<strlen($a);$i++) $out[$i]=mt_rand(0,MUTATE)?$a[$i]:$tbl[mt_rand(0,TBL_COUNT-1)];
+        return(implode('',$out));
+}
+
+
+$tbl=TBL;
+for($i=0;$i<TARGET_COUNT;$i++) $tspec[$i]=$tbl[mt_rand(0,TBL_COUNT-1)];
+$parent[0]=implode('',$tspec);
+$best=TARGET_COUNT+1;
+$iters=0;
+do {
+        for($i=1;$i<COPIES;$i++) $parent[$i]=mutate($parent[0]);
+
+        for($best_i=$i=0; $i<COPIES;$i++) {
+                $unfit=unfitness(TARGET,$parent[$i]);
+                if($unfit < $best || !$i) {
+                        $best=$unfit;
+                        $best_i=$i;
+                }
+        }
+        if($best_i>0) $parent[0]=$parent[$best_i];
+        $iters++;
+        print("Generation $iters, score $best: $parent[0]\n");
+} while($best);