平衡二叉树

输入一棵二叉树，判断该二叉树是否是平衡二叉树。

方法一：递归，每次求解left,right的深度然后做差判断。之后递归left&&right。

class Solution {
public:
    bool IsBalanced_Solution(TreeNode* pRoot) {
        if(pRoot==NULL) return true;
        int left=treedepth(pRoot->left);
        int right=treedepth(pRoot->right);
        int diff=left-right;
        if(diff>1||diff<-1)
            return false;
        return IsBalanced_Solution(pRoot->left)&&IsBalanced_Solution(pRoot->right);
    }
private:
    int treedepth(TreeNode* p){
        if(p==NULL) return 0;
        int left=treedepth(p->left);
        int right=treedepth(p->right);
        return (left>right?left+1:right+1);
    }
};

方法二：每次递归都判断是否为平衡，减少遍历次数。

class Solution {
public:
    bool IsBalanced_Solution(TreeNode* pRoot) {
        if(pRoot==NULL) return true;
        int depth=0;
        return isbalance(pRoot,&depth);
    }
private:
    bool isbalance(TreeNode* p,int * depth){
        if(p==NULL){
            *depth=0;
            return true;
        }
            
        int left;
        bool bl;
        bl=isbalance(p->left,&left);
        int right;
        bool br;
        br=isbalance(p->right,&right);
        if(bl&&br){
            *depth=left>right?left+1:right+1;
            int diff=left-right;
            if(diff>1||diff<-1)
                return false;
            else
                return true;
        }
        return false;
    }
};