Create 1028. Recover a Tree From Preorder Traversal (#723)

1028. Recover a Tree From Preorder Traversal

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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:
+    TreeNode* solve(string s, int& i, int depth) {
+        int n = s.size();
+        if (i >= n)
+            return NULL;
+
+        int j = i;
+        while (j < n && s[j] == '-') {
+            j++;
+        }
+        int dash = j - i;
+
+        if (dash != depth)
+            return NULL;
+
+        i += dash;
+        int num = 0;
+        while (i < n && isdigit(s[i])) {
+            num = num * 10 + (s[i] - '0');
+            i++;
+        }
+
+        TreeNode* root = new TreeNode(num);
+        root->left = solve(s, i, depth + 1);
+        root->right = solve(s, i, depth + 1);
+        return root;
+    }
+
+    TreeNode* recoverFromPreorder(string traversal) {
+        int i = 0;
+        return solve(traversal, i, 0);
+    }
+};