Path sum

arai60/path_sum/phase1.py

@@ -0,0 +1,9 @@
+class Solution:
+    def hasPathSum(self, root: Optional[TreeNode], targetSum: int) -> bool:
+        if not root:
+            return False
+
+        targetSum = targetSum - root.val # update targetSum
+        if targetSum == 0 and not root.right and not root.left:
+            return True
+        return self.hasPathSum(root.right, targetSum) | self.hasPathSum(root.left, targetSum)

arai60/path_sum/phase2.py

@@ -0,0 +1,33 @@
+"""
+Reference:
+fhiyo: https://github.com/fhiyo/leetcode/pull/27/files
+sakupan102: https://github.com/sakupan102/arai60-practice/pull/26#discussion_r1593805972
+
+・phase1ではtargetSumを更新して0かどうかを判断していたが, 葉だったらtargetSum == root.valかどうかを返してそれ以外はrest = targetSum - root.valとして処理する方が好みだったので書き換える。
+・|演算子よりかはor演算子の方が良いか(|はビット演算子, orの方がboolを扱う時の方では馴染みがありそう...?)
+"""
+
+class Solution:
+    def hasPathSum(self, root: Optional[TreeNode], targetSum: int) -> bool:
+        if not root:
+            return False
+
+        if not root.right and not root.left:
+            return targetSum == root.val
+        rest = targetSum - root.val # update targetSum
+        return self.hasPathSum(root.right, rest) or self.hasPathSum(root.left, rest)
+
+class Solution:
+    def hasPathSum(self, root: Optional[TreeNode], targetSum: int) -> bool:
+        stack = [(root, targetSum)]
+        while stack:
+            node, current_sum = stack.pop()
+            if not node:
+                continue
+            if not node.right and not node.left and node.val == current_sum:
+                return True
+
+            rest = current_sum - node.val
+            stack.append((node.right, rest))
+            stack.append((node.left, rest))
+        return False

arai60/path_sum/phase3.py

@@ -0,0 +1,8 @@
+class Solution:
+    def hasPathSum(self, root: Optional[TreeNode], targetSum: int) -> bool:
+        if not root:
+            return False
+        if not root.right and not root.left:
+            return targetSum == root.val
+        rest = targetSum - root.val
+        return self.hasPathSum(root.left, rest) or self.hasPathSum(root.right, rest)