September 2017 Update

Task/Quickselect-algorithm/Zkl/quickselect-algorithm-1.zkl

@@ -0,0 +1,23 @@
+fcn qselect(list,nth){	// in place quick select
+   fcn(list,left,right,nth){
+      if (left==right) return(list[left]);
+      pivotIndex:=(left+right)/2; // or median of first,middle,last
+
+      	// partition
+      pivot:=list[pivotIndex];
+      list.swap(pivotIndex,right);	// move pivot to end
+      pivotIndex := left;
+      i:=left; do(right-left){	// foreach i in ([left..right-1])
+	 if (list[i] < pivot){
+	    list.swap(i,pivotIndex);
+	    pivotIndex += 1;
+	 }
+	 i += 1;
+      }
+      list.swap(pivotIndex,right);	// move pivot to final place
+
+      if (nth==pivotIndex) return(list[nth]);
+      if (nth<pivotIndex)  return(self.fcn(list,left,pivotIndex-1,nth));
+      return(self.fcn(list,pivotIndex+1,right,nth));
+   }(list.copy(),0,list.len()-1,nth);
+}