2020-07-06

Author: JiayangWu

112.路径总和/112-路径总和.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 hasPathSum(self, root, s):
+        """
+        :type root: TreeNode
+        :type sum: int
+        :rtype: bool
+        """
+        self.res = False
+        
+        def dfs(node, pathSum):
+            if not self.res and node:
+                pathSum += node.val
+                
+                if pathSum == s and not node.left and not node.right:
+                    self.res = True
+                    return
+                
+                dfs(node.left, pathSum)
+                dfs(node.right, pathSum)
+        dfs(root, 0)
+        return self.res

276.栅栏涂色/276-栅栏涂色.py

@@ -0,0 +1,15 @@
+class Solution(object):
+    def numWays(self, n, k):
+        """
+        :type n: int
+        :type k: int
+        :rtype: int
+        """
+        dp = [0 for _ in range(n + 3)]
+        dp[0] = n
+        dp[1] = k
+        dp[2] = k * k
+        
+        for i in range(3, n + 1):
+            dp[i] = dp[i - 1] * (k - 1) + dp[i - 2] * (k - 1)
+        return dp[n]

面试题08.01.三步问题/面试题08.01-三步问题.py

@@ -0,0 +1,14 @@
+class Solution(object):
+    def waysToStep(self, n):
+        """
+        :type n: int
+        :rtype: int
+        """
+        dp = [0 for _ in range(n + 3)]
+        dp[1] = 1
+        dp[2] = 2
+        dp[3] = 4
+        MOD = 10 ** 9 + 7
+        for i in range(4, n + 1):
+            dp[i] = (dp[i - 1] + dp[i - 2] + dp[i - 3]) % MOD
+        return dp[n]

面试题16.17.连续数列/面试题16.17-连续数列.py

@@ -0,0 +1,10 @@
+class Solution(object):
+    def maxSubArray(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        dp = [0 for _ in nums]
+        for i, x in enumerate(nums):
+            dp[i] = max(x, dp[i - 1] + x) if i else x
+        return max(dp)

面试题17.16.按摩师/面试题17.16-按摩师.py

@@ -4,10 +4,11 @@ def massage(self, nums):
         :type nums: List[int]
         :rtype: int
         """
+        if not nums:
+            return 0
+        if len(nums) == 1:
+            return nums[0]
         dp = [0 for _ in nums]
-
         for i in range(len(nums)):
-            dp[i] = nums[i]
-            for j in range(i - 1):
-                dp[i] = max(dp[i], dp[j] + nums[i])
-        return max(dp) if nums else 0
+            dp[i] = max(dp[i - 1], dp[i - 2] + nums[i])
+        return dp[-1]