2020-07-15

Author: JiayangWu

0096.不同的二叉搜索树/0096-不同的二叉搜索树.py

@@ -4,12 +4,11 @@ def numTrees(self, n):
         :type n: int
         :rtype: int
         """
-        dic = {0:1, 1:1}
-
+        res = [0] * (n+1)
+        res[0] = 1
+        res[1] = 1
         for i in range(2, n + 1):
-            cnt = 0
-            for l in range(0, i):
-                cnt += dic[l] * dic[i - 1 - l]
-            dic[i] = cnt 
-
-        return dic[n]
+            for j in range(i):
+                res[i] += res[j] * res[i-j-1]
+            
+        return res[n]

0785.判断二分图/0785-判断二分图.py

@@ -0,0 +1,30 @@
+class Solution(object):
+    def isBipartite(self, graph):
+        """
+        :type graph: List[List[int]]
+        :rtype: bool
+        """
+        dic = {}
+        self.res = True
+        
+        def dfs(node):
+            if not self.res:
+                return
+            
+            for child in graph[node]:
+                # print node, child
+                if child in dic:
+                    if dic[child] == dic[node]:
+                        # print child, node, graph, dic
+                        self.res = False
+                        return
+                else:
+                    dic[child] = not dic[node]
+                    dfs(child)
+                    
+        for node in range(len(graph)):
+            if node not in dic:
+                dic[node] = True
+                dfs(node)
+        return self.res
+