2020-03-06

Author: JiayangWu

0426.将二叉搜索树转化为排序的双向链表/0426-将二叉搜索树转化为排序的双向链表.py

@@ -0,0 +1,47 @@
+"""
+# Definition for a Node.
+class Node(object):
+    def __init__(self, val, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+"""
+class Solution(object):
+    def treeToDoublyList(self, root):
+        """
+        :type root: Node
+        :rtype: Node
+        """
+        if not root:
+            return root 
+        if not root.left and not root.right:
+            root.left = root 
+            root.right = root 
+            return root 
+        
+        left = self.treeToDoublyList(root.left)
+        right = self.treeToDoublyList(root.right)
+        if root.left and root.right:
+            left_tail = left.left 
+            right_tail = right.left 
+
+            left_tail.right = root 
+            root.left = left_tail 
+            root.right = right 
+            right.left = root 
+
+            left.left = right_tail 
+            right_tail.right = left 
+        elif root.left:
+            left_tail = left.left 
+            left_tail.right = root 
+            root.left = left_tail 
+            left.left = root 
+            root.right = left 
+        elif root.right:
+            right_tail = right.left 
+            root.right = right 
+            root.left = right_tail 
+            right_tail.right = root 
+            right.left = root
+        return left if left else root

面试题35.复杂链表的复制/面试题35-复杂链表的复制.py

@@ -0,0 +1,30 @@
+"""
+# Definition for a Node.
+class Node:
+    def __init__(self, x, next=None, random=None):
+        self.val = int(x)
+        self.next = next
+        self.random = random
+"""
+class Solution(object):
+    def copyRandomList(self, head):
+        """
+        :type head: Node
+        :rtype: Node
+        """
+        mapping = {} # key is the old node, val is the new node
+
+        p = head 
+        while p:
+            mapping[p] = Node(p.val)
+            p = p.next 
+
+        p = head 
+        while p:
+            if p.next:
+                mapping[p].next = mapping[p.next]
+            if p.random:
+                mapping[p].random = mapping[p.random]
+            p = p.next
+
+        return mapping[head] if head else head

面试题36.二叉搜索树与双向链表/面试题36-二叉搜索树与双向链表.py

@@ -0,0 +1,47 @@
+"""
+# Definition for a Node.
+class Node(object):
+    def __init__(self, val, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+"""
+class Solution(object):
+    def treeToDoublyList(self, root):
+        """
+        :type root: Node
+        :rtype: Node
+        """
+        if not root:
+            return root 
+        if not root.left and not root.right:
+            root.left = root 
+            root.right = root 
+            return root 
+        
+        left = self.treeToDoublyList(root.left)
+        right = self.treeToDoublyList(root.right)
+        if root.left and root.right:
+            left_tail = left.left 
+            right_tail = right.left 
+
+            left_tail.right = root 
+            root.left = left_tail 
+            root.right = right 
+            right.left = root 
+
+            left.left = right_tail 
+            right_tail.right = left 
+        elif root.left:
+            left_tail = left.left 
+            left_tail.right = root 
+            root.left = left_tail 
+            left.left = root 
+            root.right = left 
+        elif root.right:
+            right_tail = right.left 
+            root.right = right 
+            root.left = right_tail 
+            right_tail.right = root 
+            right.left = root
+        return left if left else root

面试题38.字符串的排列/面试题38-字符串的排列.py

@@ -0,0 +1,16 @@
+class Solution(object):
+    def permutation(self, s):
+        """
+        :type s: str
+        :rtype: List[str]
+        """
+        from itertools import permutations
+        res = []
+        visited = set()
+        for item in list(permutations(s)):
+            s = "".join(item)
+            if s not in visited:
+                res.append(s)
+                visited.add(s)
+
+        return res

面试题39.数组中出现次数超过一半的数字/面试题39-数组中出现次数超过一半的数字.py

@@ -0,0 +1,7 @@
+class Solution(object):
+    def majorityElement(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        return sorted(nums)[len(nums) // 2]

面试题40.最小的k个数/面试题40-最小的k个数.py

@@ -0,0 +1,8 @@
+class Solution(object):
+    def getLeastNumbers(self, arr, k):
+        """
+        :type arr: List[int]
+        :type k: int
+        :rtype: List[int]
+        """
+        return sorted(arr)[:k]

面试题42.连续子数组的最大和/面试题42-连续子数组的最大和.py

@@ -0,0 +1,16 @@
+class Solution(object):
+    def maxSubArray(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        prefix = [0 for _ in nums]
+
+        prefix[0] = nums[0]
+        min_s = min(0, nums[0])
+        res = nums[0]
+        for i in range(1, len(nums)):
+            prefix[i] = prefix[i - 1] + nums[i]
+            res = max(prefix[i] - min_s, res)
+            min_s = min(min_s, prefix[i])
+        return res

面试题59-II.队列的最大值/面试题59-II-队列的最大值.py

@@ -0,0 +1,35 @@
+class MaxQueue(object):
+
+    def __init__(self):
+        from collections import deque
+        self.queue = deque([])
+    def max_value(self):
+        """
+        :rtype: int
+        """
+        if self.queue:
+            return max(self.queue)
+        return -1
+    
+    def push_back(self, value):
+        """
+        :type value: int
+        :rtype: None
+        """
+        self.queue.append(value)
+
+
+    def pop_front(self):
+        """
+        :rtype: int
+        """
+        if not self.queue:
+            return -1
+        return self.queue.popleft()
+
+
+# Your MaxQueue object will be instantiated and called as such:
+# obj = MaxQueue()
+# param_1 = obj.max_value()
+# obj.push_back(value)
+# param_3 = obj.pop_front()