添加0501.二叉搜索树中的众数.md迭代Java解法

problems/0501.二叉搜索树中的众数.md

@@ -429,6 +429,44 @@ class Solution {
     }
 }
 ```
+迭代法
+```java
+class Solution {
+    public int[] findMode(TreeNode root) {
+        TreeNode pre = null;
+        Stack<TreeNode> stack = new Stack<>();
+        List<Integer> result = new ArrayList<>();
+        int maxCount = 0;
+        int count = 0;
+        TreeNode cur = root;
+        while (cur != null || !stack.isEmpty()) {
+            if (cur != null) {
+                stack.push(cur);
+                cur =cur.left;
+            }else {
+                cur = stack.pop();
+                // 计数
+                if (pre == null || cur.val != pre.val) {
+                    count = 1;
+                }else {
+                    count++;
+                }
+                // 更新结果
+                if (count > maxCount) {
+                    maxCount = count;
+                    result.clear();
+                    result.add(cur.val);
+                }else if (count == maxCount) {
+                    result.add(cur.val);
+                }
+                pre = cur;
+                cur = cur.right;
+            }
+        }
+        return result.stream().mapToInt(Integer::intValue).toArray();
+    }
+}
+```
 
 ## Python