Path sum

DFS/PathSum.py

@@ -0,0 +1,59 @@
+"""
+Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.
+
+Note: A leaf is a node with no children.
+
+Example:
+
+Given the below binary tree and sum = 22,
+
+      5
+     / \
+    4   8
+   /   / \
+  11  13  4
+ /  \      \
+7    2      1
+return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.
+
+给一颗二叉树和一个值，找到从根到叶的所有路径的和中是否有一个与给定的值相当。
+
+因为只要有一个就可以了，所以直接用深度优先，最差是 O(n)。
+
+测试用例：
+https://leetcode.com/problems/path-sum/description/
+
+"""
+# 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 hasPathSum(self, root, sum):
+        """
+        :type root: TreeNode
+        :type sum: int
+        :rtype: bool
+        """
+        if not root:
+            return False
+
+        def helper(prev, root, sum):
+            if prev + root.val == sum:
+                if not root.left and not root.right:
+                    return True
+
+            if root.left:
+                if helper(prev + root.val, root.left, sum):
+                    return True
+
+            if root.right:
+                if helper(prev + root.val, root.right, sum):
+                    return True
+
+            return False
+
+        return helper(0, root, sum)

Tree/PathSumII.py

@@ -0,0 +1,66 @@
+"""
+Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.
+
+Note: A leaf is a node with no children.
+
+Example:
+
+Given the below binary tree and sum = 22,
+
+      5
+     / \
+    4   8
+   /   / \
+  11  13  4
+ /  \    / \
+7    2  5   1
+Return:
+
+[
+   [5,4,11,2],
+   [5,8,4,5]
+]
+
+PathSum 的进阶版，输出所有符合条件的路径。所以这里直接用遍历，有负数加上不是二叉搜索树应该没太多需要优化的地方。
+
+测试用例：
+https://leetcode.com/problems/path-sum-ii/description/
+
+"""
+# 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: List[List[int]]
+        """
+        if not root:
+            return []
+
+        result = []
+
+        def helper(prev, root, sum, path):
+            if prev + root.val == sum:
+                if not root.left and not root.right:
+                    result.append(list(map(int, path.split(' ')[1:]))+[root.val])
+                    return True
+
+            if root.left:
+                helper(prev + root.val, root.left, sum, path=path+" "+str(root.val))
+                    # return True
+
+            if root.right:
+                helper(prev + root.val, root.right, sum, path=path+" "+str(root.val))
+
+            return False
+
+        helper(0, root, sum, "")  
+
+        return result