feat: dutch national flag problem

elements/5_1_Dutch_National_Flag/solution.py

@@ -0,0 +1,28 @@
+# Question: Partition an array A with a pivot i such that all A[x] <= A[i] appears first
+
+
+def partition(arr, i):
+    start = 0
+    pivot = arr[i]
+    for j in range(len(arr)):
+        while start < len(arr) and arr[start] < pivot:
+            start += 1
+        if start >= len(arr):
+            break
+        if arr[j] <= pivot:
+            arr[start], arr[j] = arr[j], arr[start]
+            start += 1
+    return arr
+
+
+# Test
+def expect(a, b):
+    result = a == b
+    print("Test for " + str(a) + (" passed!" if result else " failed!"))
+
+
+a = [0, 1, 2, 0, 2, 1, 1]
+i = 3
+res = [0, 0, 1, 2, 2, 1]
+
+expect(a, partition(a, i))