Given a binary search tree (BST) with duplicates, find all the mode(s) (the most frequently occurred element) in the given BST.
Assume a BST is defined as follows:
For example:
Given BST [1,null,2,2],
1
2
/
2
return [2].
Note: If a tree has more than one mode, you can return them in any order.
Follow up: Could you do that without using any extra space? (Assume that the implicit stack space incurred due to recursion does not count).
题目含义：给一个二叉搜索树，求出现次数最多的数是哪个（哪些）
1 private int maxMode = Integer.MIN_VALUE; 2 private void readNodeValue(TreeNode root,Map<Integer,Integer> valueMap) 3 { 4 if (root == null) return; 5 valueMap.put(root.val,valueMap.getOrDefault(root.val,0)+1); 6 maxMode = Math.max(maxMode,valueMap.get(root.val)); 7 readNodeValue(root.left,valueMap); 8 readNodeValue(root.right,valueMap); 9 } 10 11 12 public int[] findMode(TreeNode root) { 13 Map<Integer,Integer> valueMap = new HashMap<>(); 14 readNodeValue(root,valueMap); 15 List<Integer> temp = new ArrayList<>(); 16 for (Map.Entry<Integer,Integer> entry:valueMap.entrySet()) 17 { 18 if (entry.getValue() == maxMode) 19 { 20 temp.add(entry.getKey()); 21 } 22 } 23 int[] modes = new int[temp.size()]; 24 for (int i=0;i<modes.length;i++) 25 { 26 modes[i] = temp.get(i); 27 } 28 return modes; 29 }
501. Find Mode in Binary Search Tree
原文：http://www.cnblogs.com/wzj4858/p/7707289.html