LeetCode(110) Balanced Binary Tree

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    int indicator = 1;
public:
    int maxDepth(TreeNode* root) {

        if(root == NULL)
            return 0;

        int leftDepth = maxDepth(root->left);
        int rightDepth = maxDepth(root->right);
        if(leftDepth > rightDepth )
            return leftDepth + 1;
        else
            return rightDepth + 1;
    }
    void check(TreeNode *root) {

        if(root == NULL)
            return;

         if(indicator == 0)
            return;

        int heightDiffer = maxDepth(root->left) - maxDepth(root->right);
        if(heightDiffer >1 || heightDiffer < -1) {
            indicator = 0;
            return;
        }
        check(root->left);
        check(root->right);
    }
    bool isBalanced(TreeNode* root) {
        check(root);
        if(indicator == 0)
            return false;
        else 
            return true;
    }
};

經過一段時間的訓練。發現上面的做法會多次遍歷同一節點。受到劍指offer P209面試題39題目二解法的啟示重寫例如以下。執行時間只為曾經的一半8ms（這一次換成了c語言。由於大多數嵌入式公司要求的是c）

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
bool isBalancedInner(struct TreeNode* root, int* height);
bool isBalanced(struct TreeNode* root)
{
    int height;
    return isBalancedInner(root, &height);
}
bool isBalancedInner(struct TreeNode* root, int* height)
{
    if(!root)
    {
        *height = 0;
        return true;
    }

    int leftHeight, rightHeight;
    bool leftIsBalanced = isBalancedInner(root->left, &leftHeight);
    bool rightIsBalanced = isBalancedInner(root->right, &rightHeight);

    if(!leftIsBalanced || !rightIsBalanced)
        return false;
    else
    {
        *height = leftHeight > rightHeight ? (leftHeight + 1) : (rightHeight + 1);
        return (leftHeight - rightHeight > 1) || (leftHeight - rightHeight < -1) ? false : true;
    }

}