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@ -177,6 +177,8 @@ public:
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## Java
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**递归**
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```Java
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class Solution {
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int sum;
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@ -198,6 +200,42 @@ class Solution {
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}
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}
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```
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**迭代**
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```Java
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class Solution {
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//DFS iteraion統一迭代法
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public TreeNode convertBST(TreeNode root) {
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int pre = 0;
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Stack<TreeNode> stack = new Stack<>();
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if(root == null) //edge case check
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return null;
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stack.add(root);
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while(!stack.isEmpty()){
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TreeNode curr = stack.peek();
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//curr != null的狀況,只負責存node到stack中
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if(curr != null){
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stack.pop();
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if(curr.left != null) //左
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stack.add(curr.left);
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stack.add(curr); //中
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stack.add(null);
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if(curr.right != null) //右
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stack.add(curr.right);
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}else{
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//curr == null的狀況,只負責做單層邏輯
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stack.pop();
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TreeNode temp = stack.pop();
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temp.val += pre;
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pre = temp.val;
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}
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}
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return root;
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}
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}
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```
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## Python
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递归法(版本一)
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