leetcode

Author: shangchun

palindrome.py

@@ -0,0 +1,25 @@
+# @param s, a string
+# @return a boolean
+def isPalindrome(s):
+    head = 0
+    tail = len(s) - 1
+    validChars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890'
+    while head < tail:
+        if s[head] not in validChars:
+            head += 1
+            continue
+        tailCode = ord(s[tail])
+        if s[tail] not in validChars:
+            tail -= 1
+            continue
+        if s[head].lower() == s[tail].lower():
+            head += 1
+            tail -= 1
+        else:
+            return False
+    return True
+
+
+assert isPalindrome("A man, a plan, a canal: Panama") == True
+assert isPalindrome("race a car") == False
+assert isPalindrome("1a2") == False

removeNthFromEnd.py

@@ -0,0 +1,43 @@
+# Definition for singly-linked list.
+class ListNode:
+    def __init__(self, x):
+        self.val = x
+        self.next = None
+
+# @return a ListNode
+def removeNthFromEnd(head, n):
+    ahead = behind = head
+    while n > 0:
+        ahead = ahead.next
+        n -= 1
+    if ahead == None:
+        node = head
+        head = head.next
+        node.next = None
+        return head;
+    while ahead.next != None:
+        ahead = ahead.next
+        behind = behind.next
+    node = behind.next
+    behind.next = node.next
+    node.next = None
+    return head
+
+a = ListNode('a')
+b = ListNode('b')
+c = ListNode('c')
+d = ListNode('d')
+e = ListNode('e')
+a.next = b
+b.next = c
+c.next = d
+d.next = e
+removeNthFromEnd(a, 2)
+assert c.next == e
+
+assert removeNthFromEnd(e, 1) == None
+
+f = ListNode('f')
+g = ListNode('g')
+f.next = g
+assert removeNthFromEnd(f, 2) == g