[LeetCode] [Balanced Binary Tree 2012-10-08 ]

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as a binary tree
in which the depth of the two subtrees of every node never differ by
more than 1.

The key problem is that recursive func should return not only T/F to indicate
if subtree is balanced, but also the depth for parent root to decide if
left/right has the same depth.

we use the TreeNode->val to store the depth, so an initialize of val is
needed at first.

?





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class
Solution {

public:

    void
ResetTree(TreeNode * root)

    {

        if(root == NULL)

        {

            return;

        }

        root->val = 0;

        ResetTree(root->left);

        ResetTree(root->right);

    }

    

    bool
treeSet = false;

    

    bool
isBalanced(TreeNode *root) {

        

        if(treeSet == false)

        {

            ResetTree(root);

            treeSet = true;

        }

        if(root == NULL)    return
true;

        

        bool
b1 = isBalanced(root->left);

        bool
b2 = isBalanced(root->right);

        if(b1 == false
|| b2 == false)

        {

            return
false;

        }

        

        int
d1 = 0;

        int
d2 = 0;

        if(root->left)

        {

            d1 = root->left->val;

        }

        if(root->right)

        {

            d2 = root->right->val;

        }

        if(d1 > d2)

        {

            root->val = d1+1;

        }

        else

        {

            root->val = d2+1;

        }

        if((d1-d2)>1 || (d1-d2)<-1)

        {

            return
false;

        }

        return
true;

    }

};

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时间： 2024-10-20 02:08:33

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