[Leetcode 105] Youngsang Solution

Leetcode/105/ysuh/solution.cpp

@@ -0,0 +1,35 @@
+/**
+ * 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:
+    map<int, int> val_idx_map;
+    int idx = 0;
+    TreeNode* find(vector<int>& preorder, vector<int>& inorder, int left, int right) {
+        if (left > right) {
+            return nullptr;
+        }
+        int i_idx = val_idx_map[preorder[idx]];
+        TreeNode* parent = new TreeNode(preorder[idx]);
+        idx++;
+        parent->left = find(preorder, inorder, left, i_idx-1);
+        parent->right = find(preorder, inorder, i_idx+1, right);
+        return parent;
+    }
+    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
+        int idx = 0;
+        for (auto ele : inorder) {
+            val_idx_map[ele] = idx;
+            idx++;
+        }
+        return find(preorder, inorder, 0, inorder.size()-1);
+    }
+};