Create Binary_Tree_Postorder_Traversal.cc

Using Morris traversal algorithm.

Author: iphkwan

Binary_Tree_Postorder_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> postorderTraversal(TreeNode *root) {
+        // IMPORTANT: Please reset any member data you declared, as
+        // the same Solution instance will be reused for each test case.
+        TreeNode *dump = new TreeNode(0);
+        dump->left = root;
+        vector<int> ret;
+        int L, R;
+        TreeNode *cur = dump, *tmp = NULL, *helper = NULL;
+        while (cur) {
+            if (!cur->left) {
+                cur = cur->right;
+            } else {
+                tmp = cur->left;
+                while (tmp->right != NULL && tmp->right != cur)
+                    tmp = tmp->right;
+                if (tmp->right != cur) {
+                    tmp->right = cur;
+                    cur = cur->left;
+                } else {
+                    //print
+                    L = ret.size();
+                    helper = cur->left;
+                    while (helper != cur) {
+                        ret.push_back(helper->val);
+                        helper = helper->right;
+                    }
+                    R = ret.size() - 1;
+                    
+                    //reverse
+                    while (L < R) {
+                        swap(ret[L++], ret[R--]);
+                    }
+                    
+                    tmp->right = NULL;
+                    cur = cur->right;
+                }
+            }
+        }
+        delete dump;
+        return ret;
+    }
+};