2020-06-18

Author: JiayangWu

1442.形成两个异或相等数组的三元组数目/1442-形成两个异或相等数组的三元组数目.py

@@ -4,17 +4,12 @@ def countTriplets(self, arr):
         :type arr: List[int]
         :rtype: int
         """
-        leftXOR = [0 for _ in arr] + [0]
-
         res = 0
-        
-        for i, x in enumerate(arr):
-            leftXOR[i + 1] = leftXOR[i] ^ x
-
-        for i in range(len(arr) + 1):
-            for j in range(i + 1, len(arr) + 1):
-                for k in range(j + 1, len(arr) + 1):
-                    if leftXOR[i] ^ leftXOR[j] == leftXOR[j] ^ leftXOR[k]:
-                        res += 1
+        for i in range(len(arr)):
+            preSum = arr[i]
+            for j in range(i + 1, len(arr)):
+                preSum ^= arr[j]
+                if not preSum:
+                    res += j - i
 
         return res

1443.收集树上所有苹果的最少时间/1443-收集树上所有苹果的最少时间.py

@@ -0,0 +1,31 @@
+class Solution(object):
+    def minTime(self, n, edges, hasApple):
+        """
+        :type n: int
+        :type edges: List[List[int]]
+        :type hasApple: List[bool]
+        :rtype: int
+        """
+        from collections import defaultdict
+        dic = defaultdict(set)
+        mustVisitNodes = set()
+        
+        for src, des in edges:
+            dic[src].add(des)
+            dic[des].add(src)
+            
+        def findMustVisitNodesDFS(node, path, visited):
+            path.append(node)
+            
+            if hasApple[node]:
+                for n in path:
+                    mustVisitNodes.add(n)
+            
+            for child in dic[node]:
+                if child not in visited:
+                    visited.add(child)
+                    findMustVisitNodesDFS(child, path + [node], visited)
+                
+        findMustVisitNodesDFS(0, [], set([0]))
+
+        return max(0, 2 * (len(mustVisitNodes) - 1))

1446.连续字符/1446-连续字符.py

@@ -0,0 +1,18 @@
+class Solution(object):
+    def maxPower(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        res = 1
+        pre = s[0]
+        tmp = 1
+        for i, ch in enumerate(s):
+            if i:
+                if ch == pre:
+                    tmp += 1
+                else:
+                    pre = ch
+                    tmp = 1
+                res = max(res, tmp)
+        return res

1447.最简分数/1447-最简分数.py

@@ -0,0 +1,11 @@
+class Solution:
+    def simplifiedFractions(self, n: int) -> List[str]:
+        import math
+        res = set()
+        
+        for down in range(1, n + 1):
+            for up in range(1, down):
+                if math.gcd(up, down) == 1:
+                    res.add(str(up) + "/" + str(down))
+                    
+        return list(res)

1448.统计二叉树中好节点的数目/1448-统计二叉树中好节点的数目.py

@@ -0,0 +1,27 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution(object):
+    def goodNodes(self, root):
+        """
+        :type root: TreeNode
+        :rtype: int
+        """
+        self.res = 0
+        
+        def dfs(node, maxVal):
+            if not node:
+                return
+            
+            if node.val >= maxVal:
+                self.res += 1
+            
+            maxVal = max(maxVal, node.val)
+            dfs(node.left, maxVal)
+            dfs(node.right, maxVal)
+        
+        dfs(root, root.val)
+        return self.res