2020-03-05

JiayangWu · JiayangWu · commit 73fa4fbc9be6 · 2020-03-05T23:01:01.000-05:00
diff --git a/面试题27.二叉树的镜像/面试题27-二叉树的镜像.py b/面试题27.二叉树的镜像/面试题27-二叉树的镜像.py
@@ -0,0 +1,19 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution(object):
+    def mirrorTree(self, root):
+        """
+        :type root: TreeNode
+        :rtype: TreeNode
+        """
+        if not root:
+            return root 
+
+        root.left, root.right = self.mirrorTree(root.right), self.mirrorTree(root.left)
+
+        return root
diff --git a/面试题28.对称的二叉树/面试题28-对称的二叉树.py b/面试题28.对称的二叉树/面试题28-对称的二叉树.py
@@ -0,0 +1,23 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution(object):
+    def isSymmetric(self, root):
+        """
+        :type root: TreeNode
+        :rtype: bool
+        """
+        if not root:
+            return True
+        
+        def check(root1, root2):
+            if not root1 and not root2:
+                return True
+            if not root1 or not root2:
+                return False
+            return root1.val == root2.val and check(root1.left, root2.right) and check(root1.right, root2.left)
+        return check(root, root)
diff --git a/面试题29.顺时针打印矩阵/面试题29-顺时针打印矩阵.py b/面试题29.顺时针打印矩阵/面试题29-顺时针打印矩阵.py
@@ -0,0 +1,45 @@
+class Solution(object):
+    def spiralOrder(self, matrix):
+        """
+        :type matrix: List[List[int]]
+        :rtype: List[int]
+        """
+        if not matrix or not matrix[0]:
+            return matrix
+        m, n = len(matrix), len(matrix[0])
+        
+        x, y = 0, 0
+        state = "r"
+        cnt = 0
+        res = []
+        visited = set()
+        while cnt < m * n:
+            res.append(matrix[x][y])
+            visited.add((x, y))
+            if state == "r":
+                if y + 1 < n and (x, y + 1) not in visited:
+                    y += 1
+                else:
+                    x += 1
+                    state = "d"
+            elif state == "d":
+                if x + 1 < m and (x + 1, y) not in visited:
+                    x += 1
+                else:
+                    y -= 1
+                    state = "l"
+            elif state == "l":
+                if y - 1 >= 0 and (x, y - 1) not in visited:
+                    y -= 1
+                else:
+                    x -= 1
+                    state = "u"
+            elif state == "u":
+                if x - 1 >= 0 and (x - 1, y) not in visited:
+                    x -= 1
+                else:
+                    y += 1
+                    state = "r"
+            cnt += 1
+        return res
+                
diff --git a/面试题30.包含min函数的栈/面试题30-包含min函数的栈.py b/面试题30.包含min函数的栈/面试题30-包含min函数的栈.py
@@ -0,0 +1,50 @@
+class MinStack(object):
+
+    def __init__(self):
+        """
+        initialize your data structure here.
+        """
+        self.stack = []
+        self.min_s = []
+
+    def push(self, x):
+        """
+        :type x: int
+        :rtype: None
+        """
+        if not self.stack:
+            self.stack = [x]
+            self.min_s = [x]
+        else:
+            self.stack.append(x)
+            if self.min_s[-1] < x:
+                self.min_s.append(self.min_s[-1])
+            else:
+                self.min_s.append(x)
+
+    def pop(self):
+        """
+        :rtype: None
+        """
+        self.stack.pop()
+        self.min_s.pop()
+
+    def top(self):
+        """
+        :rtype: int
+        """
+        return self.stack[-1]
+
+    def min(self):
+        """
+        :rtype: int
+        """
+        return self.min_s[-1]
+
+
+# Your MinStack object will be instantiated and called as such:
+# obj = MinStack()
+# obj.push(x)
+# obj.pop()
+# param_3 = obj.top()
+# param_4 = obj.min()
diff --git a/面试题31.栈的压入、弹出序列/面试题31-栈的压入、弹出序列.py b/面试题31.栈的压入、弹出序列/面试题31-栈的压入、弹出序列.py
@@ -0,0 +1,19 @@
+class Solution(object):
+    def validateStackSequences(self, pushed, popped):
+        """
+        :type pushed: List[int]
+        :type popped: List[int]
+        :rtype: bool
+        """
+        if not pushed and not popped:
+            return True
+        if not pushed or not popped:
+            return False
+        stack = []
+        popped = popped[::-1]
+        for i, num in enumerate(pushed):
+            stack.append(num)
+            while stack and stack[-1] == popped[-1]:
+                stack.pop()
+                popped.pop()
+        return not popped
diff --git a/面试题32-I.从上到下打印二叉树/面试题32-I-从上到下打印二叉树.py b/面试题32-I.从上到下打印二叉树/面试题32-I-从上到下打印二叉树.py
@@ -0,0 +1,28 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution(object):
+    def levelOrder(self, root):
+        """
+        :type root: TreeNode
+        :rtype: List[int]
+        """
+        from collections import deque
+        if not root:
+            return []
+        
+        queue = deque([root])
+        res = []
+        while queue:
+            for _ in range(len(queue)):
+                cur = queue.popleft()
+                res.append(cur.val)
+                if cur.left:
+                    queue.append(cur.left)
+                if cur.right:
+                    queue.append(cur.right)
+        return res
diff --git a/面试题32-II.从上到下打印二叉树II/面试题32-II-从上到下打印二叉树II.py b/面试题32-II.从上到下打印二叉树II/面试题32-II-从上到下打印二叉树II.py
@@ -0,0 +1,30 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution(object):
+    def levelOrder(self, root):
+        """
+        :type root: TreeNode
+        :rtype: List[List[int]]
+        """
+        from collections import deque
+        if not root:
+            return []
+        
+        queue = deque([root])
+        res = []
+        while queue:
+            tmp = []
+            for _ in range(len(queue)):
+                cur = queue.popleft()
+                tmp.append(cur.val)
+                if cur.left:
+                    queue.append(cur.left)
+                if cur.right:
+                    queue.append(cur.right)
+            res.append(tmp)
+        return res
diff --git a/面试题32-III.从上到下打印二叉树III/面试题32-III-从上到下打印二叉树III.py b/面试题32-III.从上到下打印二叉树III/面试题32-III-从上到下打印二叉树III.py
@@ -0,0 +1,35 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution(object):
+    def levelOrder(self, root):
+        """
+        :type root: TreeNode
+        :rtype: List[List[int]]
+        """
+        from collections import deque
+        if not root:
+            return []
+        
+        queue = deque([root])
+        res = []
+        flag = 1
+        while queue:
+            tmp = []
+            for _ in range(len(queue)):
+                cur = queue.popleft()
+                tmp.append(cur.val)
+                if cur.left:
+                    queue.append(cur.left)
+                if cur.right:
+                    queue.append(cur.right)
+            if flag:
+                res.append(tmp)
+            else:
+                res.append(tmp[::-1])
+            flag = 1 - flag
+        return res
diff --git a/面试题33.二叉搜索树的后序遍历序列/面试题33-二叉搜索树的后序遍历序列.py b/面试题33.二叉搜索树的后序遍历序列/面试题33-二叉搜索树的后序遍历序列.py
@@ -0,0 +1,25 @@
+class Solution(object):
+    def verifyPostorder(self, postorder):
+        """
+        :type postorder: List[int]
+        :rtype: bool
+        """
+        if not postorder or len(postorder) == 1:
+            return True
+        
+        for i in range(len(postorder)):
+            if postorder[i] > postorder[-1]:
+                break
+        if any(postorder[j] < postorder[-1] for j in range(i, len(postorder) - 1)):
+            return False
+        
+        if i == len(postorder):
+            # no right subtree
+            left = postorder[:-1]
+            right = None
+        else:
+            left = postorder[:i]
+            right = postorder[i:-1]
+            
+        return self.verifyPostorder(left) and self.verifyPostorder(right)
+            
diff --git a/面试题34.二叉树中和为某一值的路径/面试题34-二叉树中和为某一值的路径.py b/面试题34.二叉树中和为某一值的路径/面试题34-二叉树中和为某一值的路径.py
@@ -0,0 +1,31 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution(object):
+    def pathSum(self, root, summ):
+        """
+        :type root: TreeNode
+        :type sum: int
+        :rtype: List[List[int]]
+        """
+        self.res = []
+        
+        def dfs(node, path, s):
+            if not node:
+                return
+            
+            if not node.left and not node.right:
+                if s + node.val == summ:  
+                    path.append(node.val)
+                    self.res.append(path)
+                return
+            
+            dfs(node.left, path + [node.val], s + node.val)
+            dfs(node.right, path + [node.val], s + node.val)
+           
+        dfs(root, [], 0)
+        return self.res
diff --git a/面试题57-II.和为s的连续正数序列/面试题57-II-和为s的连续正数序列.py b/面试题57-II.和为s的连续正数序列/面试题57-II-和为s的连续正数序列.py
@@ -0,0 +1,22 @@
+class Solution(object):
+    def findContinuousSequence(self, target):
+        """
+        :type target: int
+        :rtype: List[List[int]]
+        """
+        from collections import deque
+        window = deque()
+        res = []
+        s = 0
+        i = 1
+        while i < target // 2 + 3:
+            if s == target:
+                res.append(list(window))
+            if s <= target:
+                window.append(i)
+                s += i
+                i += 1
+            elif s > target:
+                s -= window.popleft() 
+
+        return res
