19th Day| 530.二叉搜索树的最小绝对差,501.二叉搜索树中的众数, 236.二叉树的最近公共祖先

LeetCode 530 二叉搜索树的最小绝对差

题目链接:530.二叉树搜索树的最小绝对差

class Solution {int min = Integer.MAX_VALUE;TreeNode pre; public int getMinimumDifference(TreeNode root) {traversal(root);return min;}public void traversal(TreeNode root){if(root == null) return;traversal(root.left);if(pre != null && (root.val - pre.val) < min){min = root.val - pre.val;}pre = root;traversal(root.right);}
}

LeetCode 501 二叉搜索树中的众数

题目链接:501.二叉搜索树中的众数

class Solution {TreeNode pre;int maxTimes = 1;int currentTimes;List<Integer> list = new ArrayList<>();public int[] findMode(TreeNode root) {if(root == null) return new int[]{};traversal(root);int[] res = new int[list.size()];for(int i = 0; i < list.size(); i++){res[i] = list.get(i);}return res;}public void traversal(TreeNode root){if(root == null) return;traversal(root.left);if(pre == null || root.val != pre.val){currentTimes = 1;}if(pre != null && root.val == pre.val){currentTimes+=1;}if(currentTimes > maxTimes){list.clear();maxTimes = currentTimes;list.add(root.val);}else if(currentTimes == maxTimes){list.add(root.val);}pre = root;traversal(root.right);}
}

LeetCode 236 二叉树的最近公共祖先

题目链接:236.二叉树的最近公共祖先

class Solution {public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {if(root == null) return null;if(root.val == p.val || root.val == q.val) return root;TreeNode left = lowestCommonAncestor(root.left, p ,q);TreeNode right = lowestCommonAncestor(root.right, p, q);if(left != null && right != null) return root;if(left == null && right != null) return right;if(left != null && right == null) return left;return null;}
}