112. Path Sum

0112-path-sum/memo.md

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+### step1
+
+最初にflagをfalseでもっておいて、DFSしながら条件に合うものがあればflagをtrueにするというやり方で実装。
+
+### step2
+
+ChatGPTにflagをもたないやり方に改善してもらった。
+
+### step3
+
+3回通すまで書き直し。

0112-path-sum/step1.cpp

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+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    int flag = false;
+
+    void scan(TreeNode* root, int sum, int targetSum) {
+        if (root == nullptr) {
+            return;
+        }
+        if (root->left == nullptr && root->right == nullptr) {
+            flag = flag || (sum == targetSum);
+            return;
+        }
+        if (root->left != nullptr) {
+            scan(root->left, sum + root->left->val, targetSum);
+        }
+        if (root->right != nullptr) {
+            scan(root->right, sum + root->right->val, targetSum);
+        }
+    }
+
+    bool hasPathSum(TreeNode* root, int targetSum) {
+        if (root == nullptr) {
+            return false;
+        }
+        scan(root, root->val, targetSum);
+        return flag;
+    }
+};

0112-path-sum/step2.cpp

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+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    bool hasPathSum(TreeNode* root, int targetSum) {
+        if (root == nullptr) {
+            return false;
+        }
+
+        if (root->left == nullptr && root->right == nullptr) {
+            return root->val == targetSum;
+        }
+
+        return hasPathSum(root->left, targetSum - root->val) ||
+               hasPathSum(root->right, targetSum- root->val);
+    }
+};

0112-path-sum/step3.cpp

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+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    bool hasPathSum(TreeNode* root, int targetSum) {
+        if (root == nullptr) {
+            return false;
+        }
+        if (root->left == nullptr && root->right == nullptr) {
+            return root->val == targetSum;
+        }
+
+        return hasPathSum(root->left, targetSum - root->val) ||
+               hasPathSum(root->right, targetSum - root->val);
+    }
+};