LeetCode(剑指 Offer)- 55 - II. 平衡二叉树
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题目大意:略
解题思路:略
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AC 代码
- Java
/**
* Definition for a binary tree node.
* public class TreeNode
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) val = x;
*
*/
// 解决方案(1)
class Solution
boolean res = true;
public boolean isBalanced(TreeNode root)
dfs(root);
return res;
int dfs(TreeNode node)
if (node == null)
return 0;
int l = dfs(node.left) + 1;
int r = dfs(node.right) + 1;
if (Math.abs(l - r) > 1)
res = false;
return Math.max(l, r);
// 解决方案(2)
class Solution
public boolean isBalanced(TreeNode root)
return recur(root) != -1;
private int recur(TreeNode root)
if (root == null) return 0;
int left = recur(root.left);
if(left == -1) return -1;
int right = recur(root.right);
if(right == -1) return -1;
return Math.abs(left - right) < 2 ? Math.max(left, right) + 1 : -1;
// 解决方案(3)
class Solution
public boolean isBalanced(TreeNode root)
if (root == null) return true;
return Math.abs(depth(root.left) - depth(root.right)) <= 1 && isBalanced(root.left) && isBalanced(root.right);
private int depth(TreeNode root)
if (root == null) return 0;
return Math.max(depth(root.left), depth(root.right)) + 1;
- C++
/**
* Definition for a binary tree node.
* struct TreeNode
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL)
* ;
*/
// 解决方案(1)
class Solution
public:
bool isBalanced(TreeNode* root)
return recur(root) != -1;
private:
int recur(TreeNode* root)
if (root == nullptr) return 0;
int left = recur(root->left);
if(left == -1) return -1;
int right = recur(root->right);
if(right == -1) return -1;
return abs(left - right) < 2 ? max(left, right) + 1 : -1;
;
// 解决方案(2)
class Solution
public:
bool isBalanced(TreeNode* root)
if (root == nullptr) return true;
return abs(depth(root->left) - depth(root->right)) <= 1 && isBalanced(root->left) && isBalanced(root->right);
private:
int depth(TreeNode* root)
if (root == nullptr) return 0;
return max(depth(root->left), depth(root->right)) + 1;
;
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