110. 平衡二叉树

[Ni-Guvara]

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    bool isBalanced(TreeNode* root) {
        return getHeight(root) == -1 ? false : true;
    }

    int getHeight(TreeNode * root)
    {
        if(!root) return 0;

        int lh = getHeight(root->left);
        int rh = getHeight(root->right);

        return abs(lh - rh) > 1  || -1 == lh || -1 == rh ? -1 : max( lh , rh ) + 1; 
    }
};

[rocksc30]

迭代求深度, 递归判断平衡二叉树

/**
 * 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 boolean isBalanced(TreeNode root) {
        if(root == null) return true;
        int leftDepth = depth(root.left);
        int rightDepth = depth(root.right);

        if(Math.abs(leftDepth - rightDepth) > 1){
            return false;
        }

        return isBalanced(root.left) && isBalanced(root.right);
    }
    int depth(TreeNode root){
        if(root == null) return 0;
        LinkedList<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        int ans = 0;
        while(!queue.isEmpty()){
            ans++;
            int size = queue.size();
            for(int i = 0; i < size; i++){
                TreeNode cur = queue.poll();
                if(cur.left != null) queue.offer(cur.left);
                if(cur.right != null) queue.offer(cur.right);
            }
        }
        return ans;
    }
}