Create Binary_Tree_Preorder_Traversal.cc

using Morris traversal algorithm

Author: iphkwan

Binary_Tree_Preorder_Traversal.cc

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+/**
+ * Definition for binary tree
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    vector<int> preorderTraversal(TreeNode *root) {
+        // IMPORTANT: Please reset any member data you declared, as
+        // the same Solution instance will be reused for each test case.
+        vector<int> ret;
+        TreeNode *cur = root, *tmp = NULL;
+        while (cur) {
+            if (!cur->left) {
+                ret.push_back(cur->val);
+                cur = cur->right;
+            } else {
+                tmp = cur->left;
+                while (tmp->right && tmp->right != cur)
+                    tmp = tmp->right;
+                if (!tmp->right) {
+                    tmp->right = cur;
+                    ret.push_back(cur->val);
+                    cur = cur->left;
+                } else {
+                    tmp->right = NULL;
+                    cur = cur->right;
+                }
+            }
+        }
+        return ret;
+    }
+};