2019-08-23

Author: JiayangWu

0258.各位相加/0258-各位相加.py

@@ -4,5 +4,4 @@ def addDigits(self, num):
         :type num: int
         :rtype: int
         """
-        return 9 if num % 9 == 0 and num != 0 else num % 9
-        
+        return 1 + (num - 1) % 9 if num > 9 else num

0259.较小的三数之和/0259-较小的三数之和.py

@@ -0,0 +1,21 @@
+class Solution(object):
+    def threeSumSmaller(self, nums, target):
+        """
+        :type nums: List[int]
+        :type target: int
+        :rtype: int
+        """
+        res = 0
+        nums.sort()
+        for i, num in enumerate(nums):
+            # 现在要在比i大的下标里，找能组合出target - num 的两个数的组合
+            t = target - num
+            left, right = i + 1, len(nums) - 1
+            while left < right:
+                if nums[left] + nums[right] >= t:
+                    right -= 1 #和太大了，尝试把和缩小
+                elif nums[left] + nums[right] < t:
+                    res += right - left #在这种情况下，left可以与【left + 1， right】间任意一个数组成一组答案
+                    left += 1
+
+        return res

0260.只出现一次的数字III/0260-只出现一次的数字III.py

@@ -4,11 +4,15 @@ def singleNumber(self, nums):
         :type nums: List[int]
         :rtype: List[int]
         """
-        dic = collections.Counter(nums)
+        a, b = 0, 0
+        mask = 0
+        for num in nums:
+            mask ^= num
+        mask = mask & (-mask)
 
-        res = list()
-        for key, val in dic.items():
-            if val == 1:
-                res.append(key)
-                
-        return res
+        for num in nums:
+            if mask & num:
+                a ^= num
+            else:
+                b ^= num
+        return [a, b]

0261.以图判树/0261-以图判树.py

@@ -1,48 +1,31 @@
-
 class UnionFindSet(object):
-    def __init__(self, m):
- 
-        # m, n = len(grid), len(grid[0])
-        self.roots = [i for i in range(m)]
-        self.rank = [0 for i in range(m)]
-        self.count = m
-        
-        for i in range(m):
-            self.roots[i] = i
- 
-    def find(self, member):
-        tmp = []
-        while member != self.roots[member]:
-            tmp.append(member)
-            member = self.roots[member]
-        for root in tmp:
-            self.roots[root] = member
-        return member
+    def __init__(self, n):
+        self.count = n
+        self.roots = [i for i in range(n)]
 
+    def find(self, node):
+        while self.roots[node] != node:
+            node = self.roots[node]
+        return node
+    
     def union(self, p, q):
-        parentP = self.find(p)
-        parentQ = self.find(q)
-        if parentP != parentQ:
-            if self.rank[parentP] > self.rank[parentQ]:
-                self.roots[parentQ] = parentP
-            elif self.rank[parentP] < self.rank[parentQ]:
-                self.roots[parentP] = parentQ
-            else:
-                self.roots[parentQ] = parentP
-                self.rank[parentP] -= 1
-            self.count -= 1
-
+        p_parent = self.find(p)
+        q_parent = self.find(q)
+        self.roots[p_parent] = q_parent
+        self.count -= 1
+        
 class Solution(object):
     def validTree(self, n, edges):
         """
         :type n: int
         :type edges: List[List[int]]
         :rtype: bool
         """
+        #开并查集，如果一条边的两个顶点在放进图之前就有相同的根结点，则说明这条边放进去之后会形成一个环
         ufs = UnionFindSet(n)
-        for edge in edges:
-            if ufs.find(edge[0]) == ufs.find(edge[1]):
+        for start, end in edges:
+            if ufs.find(start) == ufs.find(end):
                 return False
-            ufs.union(edge[0], edge[1])
-            
+            ufs.union(start, end)
+        # print ufs.count
         return ufs.count == 1

0263.丑数/0263-丑数.py

@@ -0,0 +1,15 @@
+class Solution(object):
+    def isUgly(self, num):
+        """
+        :type num: int
+        :rtype: bool
+        """
+        if num <= 0:
+            return False 
+        while not num % 2:
+            num /= 2
+        while not num % 3:
+            num /= 3
+        while not num % 5:
+            num /= 5
+        return num == 1