2019-08-06

Author: JiayangWu

0225.用队列实现栈/0225-用队列实现栈.py

@@ -0,0 +1,58 @@
+class MyStack(object):
+
+    def __init__(self):
+        """
+        Initialize your data structure here.
+        """
+        self.queue1 = []
+        self.queue2 = []
+
+    def push(self, x):
+        """
+        Push element x onto stack.
+        :type x: int
+        :rtype: None
+        """
+        self.queue1.append(x)
+
+        while len(self.queue1) > 1:
+            self.queue2.append(self.queue1[0])
+            self.queue1 = self.queue1[1:]
+
+            
+        # print self.queue1, self.queue2
+    def pop(self):
+        """
+        Removes the element on top of the stack and returns that element.
+        :rtype: int
+        """
+        # print self.queue1, self.queue2
+        top = self.queue1[0]
+        self.queue1, self.queue2 = self.queue2, []
+        while len(self.queue1) > 1:
+            self.queue2.append(self.queue1[0])
+            self.queue1 = self.queue1[1:]
+        return top
+            
+
+    def top(self):
+        """
+        Get the top element.
+        :rtype: int
+        """
+        return self.queue1[0]
+        
+    def empty(self):
+        """
+        Returns whether the stack is empty.
+        :rtype: bool
+        """
+        return not self.queue1 and not self.queue2
+
+
+# Your MyStack object will be instantiated and called as such:
+# obj = MyStack()
+# obj.push(x)
+# param_2 = obj.pop()
+# param_3 = obj.top()
+# param_4 = obj.empty()

0227.基本计算器II/0227-基本计算器II.py

@@ -0,0 +1,24 @@
+import operator
+class Solution(object):
+    def calculate(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        res = []
+        calculate = {
+            "+": lambda x: res.append(x),
+            "-": lambda x: res.append(-x),
+            "*": lambda x: res.append(x * res.pop()),
+            "/": lambda x: res.append(int(operator.truediv(res.pop(), x)))
+        }
+        op = "+"
+        num = 0
+        for char in s + "+":
+            if char.isdigit():
+                num = num * 10 + int(char)
+            elif char != " ":
+                calculate[op](num)
+                op, num = char, 0
+            # print res
+        return sum(res)

0228.汇总区间/0228-汇总区间.py

@@ -7,33 +7,19 @@ def summaryRanges(self, nums):
         if not nums:
             return nums
         start, end = nums[0], nums[0]
-        
-        res = list()
-        for i, x in enumerate(nums):
-            if i == 0:
-                continue
-            
-            if x == end + 1:#代表连续
-                end = x
-            elif x != end + 1: #中断了 或者是最后一个数了
-                # print i, x, start, end
-                temp = ""
-                if start == end: #只有一个数
-                    temp += str(end)
+        res = []
+        for i, num in enumerate(nums):
+            if i != 0:
+                if num == end + 1:
+                    end += 1
                 else:
-                    temp += str(start) + "->" + str(end)
-                res.append(temp)
-                
-                start, end = x, x
-                
-            if i == len(nums) - 1:
-                temp = ""
-                if start == end: #只有一个数
-                    temp += str(end)
-                else:
-                    temp += str(start) + "->" + str(end)
-                res.append(temp)     
-                
-        # print start, end
-        return res if len(nums) > 1 else [str(nums[0])]
-            
+                    if end - start == 0:
+                        res.append(str(end))
+                    else:
+                        res.append(str(start) + "->" + str(end))
+                    start, end = num, num
+        if end - start == 0:
+            res.append(str(end))
+        else:
+            res.append(str(start) + "->" + str(end))
+        return res

0230.二叉搜索树中第K小的元素/0230-二叉搜索树中第K小的元素.py

@@ -12,15 +12,11 @@ def kthSmallest(self, root, k):
         :type k: int
         :rtype: int
         """
-        inorder = list()
-        self.inorderTra(root, inorder)
-        print inorder
 
-        return inorder[k-1]
-    
-    def inorderTra(self, node, path):
-        if not node:
-            return 
-        self.inorderTra(node.left, path)
-        path.append(node.val)
-        self.inorderTra(node.right, path)
+        def inorderTraversal(node):
+            if not node:
+                return []
+            return inorderTraversal(node.left) + [node.val] + inorderTraversal(node.right)
+        
+        l = inorderTraversal(root)
+        return l[k - 1]

0231.2的幂/0231-2的幂.py

@@ -4,8 +4,4 @@ def isPowerOfTwo(self, n):
         :type n: int
         :rtype: bool
         """
-        i = 1
-        while(i<n):
-            i*=2
-        return i == n
-        
+        return n > 0 and not (n & (n - 1))