左神基础班- 判断一颗树是否为平衡二叉树

递归套路：找出所有的可能性 。然后写代码。

ResTreeNode* isBalance(TreeNode* head){
	//注意  空树是一颗高度为0的平衡二叉树
	if(head == nullptr){
		return new ResTreeNode(true,0);
	}
	ResTreeNode* left_t = isBalance(head->left);
	if(!left_t->isB){
		return new ResTreeNode(false,0);
	}
	ResTreeNode* right_t = isBalance(head->right);
	if(!right_t->isB){
		return new ResTreeNode(false,0);
	}
	if(abs(left_t->high - right_t->high) > 1){
		return new ResTreeNode(false, 0);
	}
	return new ResTreeNode(true,left_t->high - right_t->high);
}
bool judge(TreeNode* head){
	return isBalance(head)->isB;
}

 

全代码：

#include<iostream>
#include<algorithm>
using namespace std;
struct TreeNode{
	int value;
	TreeNode* left;
	TreeNode* right;
};
struct ResTreeNode{
	bool isB;
	int high;
	ResTreeNode(bool b, int h){
		isB = b;
		high = h;
	}
};
ResTreeNode* isBalance(TreeNode* head){
	//注意  空树是一颗高度为0的平衡二叉树
	if(head == nullptr){
		return new ResTreeNode(true,0);
	}
	ResTreeNode* left_t = isBalance(head->left);
	if(!left_t->isB){
		return new ResTreeNode(false,0);
	}
	ResTreeNode* right_t = isBalance(head->right);
	if(!right_t->isB){
		return new ResTreeNode(false,0);
	}
	if(abs(left_t->high - right_t->high) > 1){
		return new ResTreeNode(false, 0);
	}
	return new ResTreeNode(true,left_t->high - right_t->high);
}
bool judge(TreeNode* head){
	return isBalance(head)->isB;
}
string getTreeWithSerial(TreeNode* head){
	if(head == nullptr){
		return "#_";
	}
	char c[8];
	sprintf(c,"%d",head->value);
	string s = c;
	s = s+ '_';
	string s1 = getTreeWithSerial(head->left);
	string s2 = getTreeWithSerial(head->right);
	return s + s1 + s2;
}
TreeNode* getTree(int arr[],int length,int i){
	if(i < length){
		TreeNode* Treenode = new TreeNode();
		Treenode->value = arr[i];
		if((2*i+1) < length){
			Treenode->left = getTree(arr, length, 2*i+1);
		}else{
			Treenode->left = nullptr;
		}
		if((2*i+2)<length){
			Treenode->right = getTree(arr, length,2*i+2);
		}else{
			Treenode->right = nullptr;
		}
		return Treenode;
	}
	return nullptr;
}
int main(){
	int arr[] = {5,3,8,2,4,6,9,1};
	// int arr[] = {1,2,3};
	int length = sizeof(arr)/sizeof(arr[0]);
	//建树
	TreeNode* head = getTree(arr, length,0);
	//前序查看建树是否正确
	string str = getTreeWithSerial(head);
	//查看是否是平衡二叉树
	cout << judge(head);
	// cout <<str;
	// cout << head->right->value;
	return 0;
}