Thursday, September 19, 2013

104. Maximum Depth of Binary Tree (easy)

Q:

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.
Note: A leaf is a node with no children.
Example:
Given binary tree [3,9,20,null,null,15,7],
    3
   / \
  9  20
    /  \
   15   7
return its depth = 3.

A:

/**
 * 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) {
        if(!root)
            return 0;
        return 1+ max(maxDepth(root->left), maxDepth(root->right));
    }
};

Learned:
注意,以前的一个错误。 就是,null也可以作为参数传递给方法。
也就是说,上面的代码, 当root.left == null 的时候,依然正确。


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