中国最好的网站建设公司,企业网站制作服务器,如何查询自己的企业邮箱,网站的模块文章目录 Leetcode 110.平衡二叉树解题思路代码总结 Leetcode 257. 二叉树的所有路径解题思路代码总结 Leetcode 404.左叶子之和解题思路代码总结 草稿图网站 java的Deque
Leetcode 110.平衡二叉树 题目#xff1a;** 110.平衡二叉树** 解析#xff1a;代码随想录解析 解题思… 文章目录 Leetcode 110.平衡二叉树解题思路代码总结 Leetcode 257. 二叉树的所有路径解题思路代码总结 Leetcode 404.左叶子之和解题思路代码总结 草稿图网站 java的Deque
Leetcode 110.平衡二叉树 题目** 110.平衡二叉树** 解析代码随想录解析 解题思路
求高度的方法加一点判断
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;* }* }*///使用求高度来代替使用-1来减枝
class Solution {public boolean isBalanced(TreeNode root) {return getHeight(root) ! -1;}public int getHeight(TreeNode root) {if (root null) return 0;int leftHeight getHeight(root.left);if (leftHeight -1) return -1;int rightHeight getHeight(root.right);if (rightHeight -1) return -1;if (Math.abs(leftHeight-rightHeight) 1)return -1;return Math.max(leftHeight, rightHeight) 1;}
}总结
暂无
Leetcode 257. 二叉树的所有路径 题目257. 二叉树的所有路径 解析代码随想录解析 解题思路
使用回溯法的思想终止条件叶子节点遍历递归前加入元素递归结束删除元素
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;* }* }*///回溯
class Solution {public ListString binaryTreePaths(TreeNode root) {ListString res new ArrayListString();if (root null)return res;ListInteger paths new ArrayListInteger();traversal(root, res, paths);return res;}private void traversal(TreeNode node, ListString res, ListInteger paths){paths.add(node.val);if (node.left null node.right null){StringBuilder sb new StringBuilder();sb.append(paths.get(0));for (int i 1; i paths.size(); i)sb.append(- paths.get(i));res.add(sb.toString());return;}if (node.left ! null){traversal(node.left, res, paths);paths.remove(paths.size()-1);}if (node.right ! null){traversal(node.right, res, paths);paths.remove(paths.size()-1);}}
}//不用公共paths版的回溯
class Solution {public ListString binaryTreePaths(TreeNode root) {ListString res new ArrayListString();traversal(root, res, );return res;}private void traversal(TreeNode node, ListString res, String paths){if (node null)return;if (node.left null node.right null){res.add(new StringBuilder(paths).append(node.val).toString());return;}String tmp new StringBuilder(paths).append(node.val).append(-).toString();if (node.left ! null)traversal(node.left, res, tmp);if (node.right ! null)traversal(node.right, res, tmp);}
}总结
回溯大法好
Leetcode 404.左叶子之和 题目404.左叶子之和 解析代码随想录解析 解题思路
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 {public int sumOfLeftLeaves(TreeNode root) {if (root null)return 0;int leftSum sumOfLeftLeaves(root.left);int rightSum sumOfLeftLeaves(root.right);if (root.left ! null root.left.left null root.left.right null)leftSum root.left.val;return leftSum rightSum;}
}//迭代就是普通的遍历
class Solution {public int sumOfLeftLeaves(TreeNode root) {if (root null)return 0;int res 0;StackTreeNode stack new StackTreeNode();stack.push(root);while (!stack.isEmpty()){TreeNode node stack.pop();if (node.left ! null node.left.left null node.left.right null)res node.left.val;if (node.left ! null) stack.push(node.left);if (node.right ! null) stack.push(node.right);}return res;}
}总结
二叉树递归还得多学学多思考
