LeetCode OJ刷題歷程——Maximum Depth of Binary Tree

Given a binary tree, find its maximum depth.
The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.
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以上是題目要求，下面貼出代碼：

/**
 * 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 {
public:
    int maxDepth(TreeNode* root) {
        int left,right;
        if(root == NULL)
            return 0;
        left = maxDepth(root->left) + 1;
        right = maxDepth(root->right) + 1;
        return max(left,right);
    }
};

此題考點爲二叉樹的深度優先遍歷，利用遞歸最爲容易理解。根的深度等於max(左子樹和右子樹的深度)+1，同時左子樹的深度又可以用同樣的公式來表示，因此可以用遞歸來求解。葉子節點的深度爲1.