Update

Author: applewjg

FlattenBinaryTreetoLinkedList.h

@@ -1,7 +1,7 @@
 /*
- Author:     Annie Kim, [email protected]
+ Author:     Annie Kim, [email protected] : King, [email protected]
  Date:       Apr 28, 2013
- Update:     Sep 29, 2013
+ Update:     Oct 7, 2014
  Problem:    Flatten Binary Tree to Linked List
  Difficulty: Medium
  Source:     http://leetcode.com/onlinejudge#question_114
@@ -27,7 +27,7 @@
           \
            6
  Hints:
- If you notice carefully in the flattened tree, each node's right child points to the next node 
+ If you notice carefully in the flattened tree, each node's right child points to the next node
  of a pre-order traversal.
 
  Solution: Recursion. Return the last element of the flattened sub-tree.
@@ -45,10 +45,52 @@
 class Solution {
 public:
     void flatten(TreeNode *root) {
+        flatten_3(root);
+    }
+
+    void flatten_1(TreeNode *root) {
+        if (root == NULL) return;
+        flatten_1(root->left);
+        flatten_2(root->right);
+        if (root->left == NULL) return;
+        TreeNode *p = root->left;
+        while (p->right) p = p->right;
+        p->right = root->right;
+        root->right = root->left;
+        root->left = NULL;
+    }
+
+    TreeNode * dfs (TreeNode * root, TreeNode * tail){
+        if(root == NULL) return tail;
+        root->right = dfs(root->left,dfs(root->right,tail));
+        root->left = NULL;
+        return root;
+    }
+    void flatten_2(TreeNode *root) {
+        if(root == NULL) return;
+        dfs(root, NULL);
+    }
+    void flatten_3(TreeNode *root) {
+        if(root==nullptr) return;
+        stack<TreeNode*> s;
+        s.push(root);
+        while(!s.empty()){
+            auto p=s.top();
+            s.pop();
+            if(p->right) s.push(p->right);
+            if(p->left) s.push(p->left);
+            p->left = nullptr;
+            if(!s.empty()){
+                p->right=s.top();
+            }else p->right = nullptr;
+        }
+    }
+
+    void flatten_4(TreeNode *root) {
         TreeNode *end = NULL;
         flattenRe(root, end);
     }
-    
+
     void flattenRe(TreeNode *node, TreeNode *&end) {
         if (!node) return;
         TreeNode *lend = NULL, *rend = NULL;