新增 Java 統一迭代法

新增 Java 統一迭代法

problems/0501.二叉搜索树中的众数.md

@@ -472,6 +472,59 @@ class Solution {
     }
 }
 ```
+統一迭代法
+```Java
+class Solution {
+    public int[] findMode(TreeNode root) {
+        int count = 0;
+        int maxCount = 0;
+        TreeNode pre = null;
+        LinkedList<Integer> res = new LinkedList<>();
+        Stack<TreeNode> stack = new Stack<>();
+
+        if(root != null)
+            stack.add(root);
+        
+        while(!stack.isEmpty()){
+            TreeNode curr = stack.peek();
+            if(curr != null){
+                stack.pop();
+                if(curr.right != null)
+                    stack.add(curr.right);
+                stack.add(curr);
+                stack.add(null);
+                if(curr.left != null)
+                    stack.add(curr.left);
+            }else{
+                stack.pop();
+                TreeNode temp = stack.pop();
+                if(pre == null)
+                    count = 1;
+                else if(pre != null && pre.val == temp.val)
+                    count++;
+                else
+                    count = 1;
+                pre = temp;
+                if(count == maxCount)
+                    res.add(temp.val);
+                if(count > maxCount){
+                    maxCount = count;
+                    res.clear();
+                    res.add(temp.val);
+                }
+            }
+        }
+        int[] result = new int[res.size()];
+        int i = 0;
+        for (int x : res){
+            result[i] = x;
+            i++;
+        }
+        return result;    
+    }
+}
+```
+
 
 ## Python