112. Path Sum

112/step1.cpp

@@ -0,0 +1,21 @@
+/*
+Solve Time : 03:57
+
+Time : O(N)
+Space : O(N)
+
+再帰でざっくりと実装、特に悩むことなく実装完了
+*/
+class Solution {
+public:
+  bool hasPathSum(TreeNode* root, int target_sum) {
+    if (!root) {
+      return false;
+    }
+    if (!root->left && !root->right) {
+      return target_sum == root->val;
+    }
+    return hasPathSum(root->left, target_sum - root->val) || hasPathSum(root->right, target_sum - root->val);
+  }
+};
+

112/step2.cpp

@@ -0,0 +1,26 @@
+/*
+Time : O(N)
+Space : O(N)
+
+再帰ではなく、stackを使って実装
+*/
+class Solution {
+public:
+  bool hasPathSum(TreeNode* root, int target_sum) {
+    stack<pair<TreeNode*, int>> nodes_and_sums;
+    nodes_and_sums.emplace(root, target_sum);
+    while (!nodes_and_sums.empty()) {
+      auto [node, sum] = nodes_and_sums.top();
+      nodes_and_sums.pop();
+      if (!node) {
+        continue;
+      }
+      if (!node->left && !node->right && sum == node->val) {
+        return true;
+      }
+      nodes_and_sums.emplace(node->left, sum - node->val);
+      nodes_and_sums.emplace(node->right, sum - node->val);
+    }
+    return false;
+  }
+};

112/step3.cpp

@@ -0,0 +1,12 @@
+class Solution {
+public:
+  bool hasPathSum(TreeNode* root, int target_sum) {
+    if (!root) {
+      return false;
+    }
+    if (!root->left && !root->right) {
+      return target_sum == root->val;
+    }
+    return hasPathSum(root->left, target_sum - root->val) || hasPathSum(root->right, target_sum - root->val);
+  }
+};