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kedebug · kedebug · commit fd3228acd6e8 · 2014-09-22T15:24:09.000+08:00
diff --git a/BinaryTreePreorderTraversal/BinaryTreePreorderTraversal.cpp b/BinaryTreePreorderTraversal/BinaryTreePreorderTraversal.cpp
@@ -0,0 +1,36 @@
+/**
+ * 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) {
+        vector<int> result;
+        TreeNode* node = root;
+        while (node) {
+            if (node->left == NULL) {
+                result.push_back(node->val);
+                node = node->right;
+            } else {
+                TreeNode* next = node->left;
+                while (next->right && next->right != node) {
+                    next = next->right;
+                }
+                if (next->right == NULL) {
+                    next->right = node;
+                    result.push_back(node->val);
+                    node = node->left;
+                } else {
+                    next->right = NULL;
+                    node = node->right;
+                }
+            }
+        }
+        return result;
+    }
+};
