QuickSelect.py finally approved

Author: armanjscript

DataStructures/Section11/QuickSelect.py

@@ -0,0 +1,38 @@
+#Finding Kth smallest value in list by selection algorithms
+
+def quick_select(array_list, start, end, k):
+    split = partition(array_list, start, end)
+    if split == k:
+        return array_list[split]
+    elif split < k:
+        return quick_select(array_list, split + 1, end, k)
+    else:
+        return quick_select(array_list, start, split - 1, k)
+
+
+def partition(unsorted_array, first_index, last_index):
+    pivot = unsorted_array[first_index]
+    pivot_index = first_index
+    index_of_last_element = last_index
+    less_than_pivot_index = index_of_last_element
+    greater_than_pivot_index = first_index + 1
+    while True:
+        while unsorted_array[greater_than_pivot_index] < pivot and greater_than_pivot_index < last_index:
+            greater_than_pivot_index += 1
+        while unsorted_array[less_than_pivot_index] > pivot and less_than_pivot_index >= first_index:
+            less_than_pivot_index -= 1
+        if greater_than_pivot_index < less_than_pivot_index:
+            temp = unsorted_array[greater_than_pivot_index]
+            unsorted_array[greater_than_pivot_index] = unsorted_array[less_than_pivot_index]
+            unsorted_array[less_than_pivot_index] = temp
+        else:
+            break
+    unsorted_array[pivot_index] = unsorted_array[less_than_pivot_index]
+    unsorted_array[less_than_pivot_index] = pivot
+    return less_than_pivot_index
+
+
+list1 = [3,1,10, 4, 6, 5]
+print("The 2nd smallest element is", quick_select(list1, 0, 5, 1))
+print("The 3rd smallest element is", quick_select(list1, 0, 5, 2))
+