2019-07-21

Author: JiayangWu

0172.阶乘后的零/0172-阶乘后的零.py

@@ -0,0 +1,12 @@
+class Solution(object):
+    def trailingZeroes(self, n):
+        """
+        :type n: int
+        :rtype: int
+        """
+        res = 0
+        while n > 4:
+            n //= 5
+            res += n
+        return res
+        

5130.等价多米诺骨牌对的数量/5130-等价多米诺骨牌对的数量.py

@@ -0,0 +1,17 @@
+class Solution(object):
+    def numEquivDominoPairs(self, dominoes):
+        """
+        :type dominoes: List[List[int]]
+        :rtype: int
+        """
+        from collections import defaultdict
+        dic = defaultdict(int)
+        res = 0
+        for i, x in enumerate(dominoes):
+            pair = (x[1], x[0])
+            if x[0] < x[1]:
+                pair = (x[0], x[1])
+            res += dic[pair]
+            dic[pair] += 1
+            
+        return res

5132.颜色交替的最短路径/5132-颜色交替的最短路径.py

@@ -0,0 +1,40 @@
+class Solution(object):
+    def shortestAlternatingPaths(self, n, red_edges, blue_edges):
+        """
+        :type n: int
+        :type red_edges: List[List[int]]
+        :type blue_edges: List[List[int]]
+        :rtype: List[int]
+        """
+        from collections import defaultdict, deque
+        red_nei, blue_nei = defaultdict(set), defaultdict(set)
+        
+        for start, end in red_edges: #记录下所有的从红色路径可以到达的邻居节点
+            red_nei[start].add(end)
+        for start, end in blue_edges: #记录下所有的从蓝色路径可以到达的邻居节点
+            blue_nei[start].add(end)
+            
+        visited = set()
+        queue = deque()
+        queue.append((0, -1)) # -1 无色， 0 红色， 1蓝色
+        distance = 0
+        res = [-1] * n
+        while queue:
+            next_queue = deque()
+            for cur, color in queue:
+                if res[cur] == -1: #BFS保障了第一次到达终点时的距离一定是最短距离
+                    res[cur] = distance
+                if color == -1 or color == 0: #当前是红色，下一次在蓝色里找
+                    for nei in blue_nei[cur]:
+                        if (cur, nei, 1) not in visited:
+                            visited.add((cur, nei, 1))
+                            next_queue.append((nei, 1))
+                if color == -1 or color == 1: #当前是蓝色，下一次在红色里找
+                    for nei in red_nei[cur]:
+                        if (cur, nei, 0) not in visited:
+                            visited.add((cur, nei, 0))
+                            next_queue.append((nei, 0))
+            queue = next_queue
+            distance += 1
+        return res
+        

5133.绝对值表达式的最大值/5133-绝对值表达式的最大值.py

@@ -0,0 +1,34 @@
+class Solution(object):
+    def maxAbsValExpr(self, arr1, arr2):
+        """
+        :type arr1: List[int]
+        :type arr2: List[int]
+        :rtype: int
+        """
+        record = [-2 ** 31] * 8
+        
+        for i in range(len(arr1)):
+            for k in range(8): #生成八种可能的结果
+                t = 0
+                if k & 1:
+                    t += arr1[i]
+                else:
+                    t -= arr1[i]
+                if k & 2:
+                    t += arr2[i]
+                else:
+                    t -= arr2[i]
+                if k & 4:
+                    t += i
+                else:
+                    t -= i
+                # print k, t
+                record[k] = max(record[k], t)
+        # print record
+        res = 0    
+        for k in range(8):
+            # print k, ~k
+            res = max(res, record[k] + record[-k-1]) #第一项和最后一项，第二项和倒数第二项，两项之和一定是满足表达式的
+        return res
+                
+