@@ -153,23 +153,27 @@ public:
153153递归
154154```java
155155class Solution {
156- TreeNode pre;// 记录上一个遍历的结点
156+ TreeNode pre;// 记录上一个遍历的结点
157157 int result = Integer.MAX_VALUE;
158+
158159 public int getMinimumDifference(TreeNode root) {
159- if(root==null)return 0;
160- traversal(root);
161- return result;
160+ if (root == null)
161+ return 0;
162+ traversal(root);
163+ return result;
162164 }
163- public void traversal(TreeNode root){
164- if(root==null)return;
165- //左
165+
166+ public void traversal(TreeNode root) {
167+ if (root == null)
168+ return;
169+ // 左
166170 traversal(root.left);
167- //中
168- if(pre!= null){
169- result = Math.min(result,root.val- pre.val);
171+ //中
172+ if(pre != null){
173+ result = Math.min(result,root.val - pre.val);
170174 }
171175 pre = root;
172- //右
176+ //右
173177 traversal(root.right);
174178 }
175179}
@@ -182,22 +186,27 @@ class Solution {
182186 TreeNode pre = null ;
183187 int result = Integer . MAX_VALUE
184188
185- if (root != null )
189+ if (root != null )
186190 stack. add(root);
187- while (! stack. isEmpty()){
191+ 192+ // 中序遍历(左中右),由于栈先入后出,反序(右中左)
193+ while (! stack. isEmpty()) {
188194 TreeNode curr = stack. peek();
189- if (curr != null ){
195+ if (curr != null ){
190196 stack. pop();
191- if (curr. right != null )
197+ // 右
198+ if (curr. right != null )
192199 stack. add(curr. right);
200+ // 中(先用null标记)
193201 stack. add(curr);
194202 stack. add(null );
195- if (curr. left != null )
203+ // 左
204+ if (curr. left != null )
196205 stack. add(curr. left);
197- }else {
206+ }else { // 中(遇到null再处理)
198207 stack. pop();
199208 TreeNode temp = stack. pop();
200- if (pre != null )
209+ if (pre != null )
201210 result = Math . min(result, temp. val - pre. val);
202211 pre = temp;
203212 }
@@ -674,3 +683,4 @@ public class Solution
674683<a href =" https://programmercarl.com/other/kstar.html " target =" _blank " >
675684 <img src =" ../pics/网站星球宣传海报.jpg " width =" 1000 " />
676685</a >
686+
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