代码随想录 Day21 - 二叉树（七）

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode() {} *     TreeNode(int val) { this.val = val; } *     TreeNode(int val, TreeNode left, TreeNode right) { *         this.val = val; *         this.left = left; *         this.right = right; *     } * } */class Solution {    private TreeNode pre;    private int minDifference;        public int getMinimumDifference(TreeNode root) {        this.minDifference = Integer.MAX_VALUE;        traversal(root);        return minDifference;    }        private void traversal(TreeNode current) {        if (current == null) {            return;        }        traversal(current.left);        if (pre != null) {            minDifference = Math.min(minDifference, current.val - pre.val);        }        pre = current;        traversal(current.right);    }}

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode() {} *     TreeNode(int val) { this.val = val; } *     TreeNode(int val, TreeNode left, TreeNode right) { *         this.val = val; *         this.left = left; *         this.right = right; *     } * } */class Solution {    private List<Integer> result;    private int maxCount;    private int curCount;    private TreeNode pre;        public int[] findMode(TreeNode root) {        this.result = new ArrayList<>();        traversal(root);        int[] res = new int[result.size()];        for (int i = 0; i < result.size(); i++) {            res[i] = result.get(i);        }        return res;    }        private void traversal(TreeNode current) {        if (current == null) {            return;        }        traversal(current.left);        if (result.isEmpty() && maxCount == 0) {            result.add(current.val);        }        int curVal = current.val;        if (pre == null || curVal != pre.val) {            curCount = 1;        } else {            curCount++;        }        if (curCount > maxCount) {            result = new ArrayList<>();            result.add(curVal);            maxCount = curCount;        } else if (curCount == maxCount) {            result.add(curVal);        }        pre = current;        traversal(current.right);    }}

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */class Solution {     public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {        if (root == null || root == p || root == q) { // 递归结束条件            return root;        }                // 后序遍历        TreeNode left = lowestCommonAncestor(root.left, p, q);        TreeNode right = lowestCommonAncestor(root.right, p, q);                if (left == null && right == null) { // 若未找到节点 p 或 q            return null;        } else if (left == null) { // 若找到一个节点            return right;        } else if (right == null) { // 若找到一个节点            return left;        } else { // 若找到两个节点            return root;        }    }    }