110Balanced Binary Tree

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int flag=true;
    int dfs(TreeNode *root)
    {
         if(root==NULL) return true;
         int h1,h2;
         if(root->left==NULL) h1=0;
         else h1=dfs(root->left);
         if(root->right==NULL) h2=0;
         else h2=dfs(root->right);
         if(abs(h1-h2)>1) flag=0;
         return max(h1,h2)+1;
    }
    bool isBalanced(TreeNode *root) {
        dfs(root);
        return flag;
    }
};

/**
 * 题意：判断二叉树是否为平衡二叉树
 * 分析：枚举节点判断其左子树的高度和右子树的高度差是否小于1
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isBalanced = function(root) {
    flag = true;
    if(root == null) return true;
    var left = DFS(root.left);
    var right = DFS(root.right);
      if(Math.abs(left-right)>1) {
       flag = false;
   }
    return flag;
};

flag = true;
function DFS(root){
   if(root == null) return 0;
   var left = DFS(root.left) +1;
   var right = DFS(root.right) +1;
   if(Math.abs(left-right)>1) {
       flag = false;
   }
   return Math.max(left,right);
}

/**
 * 题意：判断二叉树是否为平衡二叉树
 * 分析：枚举节点判断其左子树的高度和右子树的高度差是否小于1
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isBalanced = function(root) {
    if(root == null) return true;
    return DFS(root) != -1;
};

function DFS(root){
   if(root == null) return 0;
   var left = DFS(root.left);
   var right = DFS(root.right);
   if(left==-1 || right==-1 || Math.abs(left-right)>1) {//-1表示存在不平衡的情况
       return -1;
   }
   return Math.max(left,right) + 1;
}