前言
###我做这类文章一个重要的目的还是给正在学习的大家提供方向（例如想要掌握基础用法，该刷哪些题？建议灵神的题单和代码随想录）和记录自己的学习过程，我的解析也不会做的非常详细，只会提供思路和一些关键点，力扣上的大佬们的题解质量是非常非常高滴！！！
习题
1.最深叶节点的最近公共祖先
题目链接:1123. 最深叶节点的最近公共祖先 - 力扣（LeetCode）
题面:
代码:
/*** 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 {int maxdep = 0;TreeNode ans = null;int sum = 0;public TreeNode lcaDeepestLeaves(TreeNode root) {recursion2(root,0);// System.out.println(maxdep+" "+sum);recursion(root,0);return ans;}public int recursion(TreeNode node,int dep){if(node==null){return 0;}if(node.left==null&&node.right==null){if(dep==maxdep){if(sum==1){ans = node;return 99999;}return 1;}return 0;}int l = recursion(node.left,dep+1);int r = recursion(node.right,dep+1);if((l+r)==sum){ans = node;return 99999;}return (l+r);}public void recursion2(TreeNode node,int dep){if(node==null){return;}if(node.left==null&&node.right==null){if(dep>maxdep){maxdep = dep;sum = 1;}else if(maxdep==dep){sum++;}}recursion2(node.left,dep+1);recursion2(node.right,dep+1);}
}2.从二叉树一个节点到另一个节点的每一步的方向
题目链接:2096. 从二叉树一个节点到另一个节点每一步的方向 - 力扣（LeetCode）
题面:
注意递归遍历树的时候别在参数拼接树，当树太大会OOM，用StringBuilder
代码:
/*** 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 {TreeNode linP = null;int startValue;int destValue;String start = "";String dest = "";public String getDirections(TreeNode root, int startValue, int destValue) {this.startValue = startValue;this.destValue = destValue;int sign = recursion2(root);if(sign==2){linP = root;}StringBuilder sb = new StringBuilder();recursion(linP,sb);// System.out.println(start+" "+dest);int size = start.length();String ans = "";while(size>0){size--;ans+="U";}if(dest.equals("")){return ans;}if(start.equals("")){return dest;}return ans+dest;}public void recursion(TreeNode node,StringBuilder sb){if(!dest.equals("")&&!start.equals(""))return;if(node==null)return;if(node.val==startValue){start = sb.toString();}else if(node.val==destValue){dest = sb.toString();}recursion(node.left,sb.append("L"));sb.deleteCharAt(sb.length()-1);recursion(node.right,sb.append("R"));sb.deleteCharAt(sb.length()-1);}public int recursion2(TreeNode node){if(linP!=null)return 99999;if(node==null)return 0;int l = recursion2(node.left);int r = recursion2(node.right);if(node.val==startValue||node.val==destValue){int sum = l+r+1;if(sum==2){linP = node;return 9999;}return sum;}if((l+r)==2){linP = node;return 99999;}return l+r;}
}后言
上面是数据结构相关的习题，下一篇文章会将其他相关的习题。
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