python: add problem 24,27 and unittest

Author: supercoderhawk

Python/common_utils.py

@@ -0,0 +1,16 @@
+# -*- coding: utf-8 -*
+class ListNode:
+    def __init__(self, x):
+        self.val = x
+        self.next = None
+
+
+def print_linked_list(head):
+    node = head
+    s = ''
+    while node:
+        s += str(node.val)
+        if node.next:
+            s += '->'
+        node = node.next
+    print(s)

Python/sln_1_100/__init__.py

@@ -0,0 +1 @@
+# -*- coding: utf-8 -*-

Python/sln_1_100/solution_21_30.py

@@ -0,0 +1,51 @@
+# -*- coding: utf-8 -*-
+from common_utils import ListNode
+
+
+class Solution_21_30(object):
+    def swapPairs(self, head):
+        """
+        24
+        :param head:
+        :return:
+        """
+        if not head or not head.next:
+            return head
+        prev_node = node = head
+        is_start = True
+        while node:
+            if not node.next:
+                break
+            next_node = node.next
+            node.next = next_node.next
+
+            next_node.next = node
+
+            if is_start:
+                head = next_node
+                is_start = False
+            else:
+                prev_node.next = next_node
+            prev_node = node
+            node = node.next
+
+        return head
+
+    def removeElement(self, nums, val):
+        """
+        27
+        :type nums: List[int]
+        :type val: int
+        :rtype: int
+        """
+        count = index = 0
+        original_nums_len = nums_len = len(nums)
+        while index < nums_len:
+            if nums[index] == val:
+                nums.pop(index)
+                count += 1
+                nums_len -= 1
+            else:
+                index += 1
+
+        return original_nums_len - count

Python/sln_1_100/test_solution_21_30.py

@@ -0,0 +1,27 @@
+# -*- coding: utf-8 -*-
+from unittest import TestCase
+from sln_1_100.solution_21_30 import Solution_21_30
+from common_utils import ListNode, print_linked_list
+
+
+class TestSolution_21_30(TestCase):
+    def setUp(self):
+        self.sln = Solution_21_30()
+
+    def test_swapPairs(self):
+        node1 = ListNode(1)
+        node2 = ListNode(2)
+        node1.next = node2
+        node3 = ListNode(3)
+        node2.next = node3
+        node4 = ListNode(4)
+        node3.next = node4
+        print_linked_list(node1)
+        # node = self.sln.swapPairs(node1)
+        node = self.sln.swapPairs(node2)
+        print_linked_list(node)
+
+    def test_removeElement(self):
+        ret = self.sln.removeElement([1, 2, 2, 3, 4, 5], 2)
+        self.assertEqual(ret, 2)
+        ret2 = self.sln.removeElement([1], 1)