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Author: whd

437 Path Sum III .py

@@ -0,0 +1,34 @@
+# 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 pathSum(self, root, sum):
+        """
+        :type root: TreeNode
+        :type sum: int
+        :rtype: int
+        """
+        ans = 0
+        dic = {}
+        dic[0] = 1
+        global ans
+        def dfs(x, now):
+            global ans
+            if not x:
+                return
+            now += x.val
+            if (now - sum) in dic:
+                ans += dic[now - sum]
+            if not now in dic:
+                dic[now] = 0
+            dic[now] += 1
+            dfs(x.left, now)
+            dfs(x.right, now)
+            dic[now] -= 1
+        
+        dfs(root, 0)
+        return ans