二叉树题目----5 平衡二叉树 AND 根据二叉树创建字符串

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本文链接： https://blog.csdn.net/liuyuchen282828/article/details/102404003

平衡二叉树

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */

int MAX(int a,int b)
{
    return a > b ? a : b;
}

//求高度
int getHeight(struct TreeNode *root){
    if(root == NULL){
        return 0;
    }

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

    return MAX(left,right)+1;
}
bool isBalanced(struct TreeNode* root){
    if(root == NULL){
        return true;
    }
    //左子树是不是平衡二叉树
        bool is_left_balance =isBalanced(root->left);
        if(is_left_balance == false){
            return false;
        }
	//右子树是不是平衡二叉树
        bool is_right_balance =isBalanced(root->right);
        if(is_right_balance == false){
            return false;
        }
        int left_height = getHeight(root->left);
        int right_height = getHeight(root->right);
        int diff =left_height-right_height;
	//左右子树高度差要小于1	
        if(diff >= -1 && diff <=1){
            return true;
        }else{
            return false;
        }
}

根据二叉树创建字符串

class Solution {
public:
    string tree2str(TreeNode* t) {
        if(t==nullptr)
            return "";
        stringstream ss;
        function<void(TreeNode*)> helper = [&ss, &helper](TreeNode* t){
            ss<<t->val;
            if(t->left==nullptr){
                if(t->right!=nullptr){
                    ss<<"()(";
                    helper(t->right);
                    ss<<')';
                }
            }
            else if(t->right==nullptr){
                ss<<'(';
                helper(t->left);
                ss<<')';
            }
            else{
                ss<<'(';
                helper(t->left);
                ss<<")(";
                helper(t->right);
                ss<<')';
            }
        };
        helper(t);
        string s;
        ss>>s;
        return s;
    }
};