Lintcode 97.二叉树的最大深度

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AC代码：

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
    public int maxDepth(TreeNode root) {
        if(root==null) return 0;
        return Math.max(maxDepth(root.left),maxDepth(root.right))+1;
    }
}

题目来源： http://www.lintcode.com/zh-cn/problem/maximum-depth-of-binary-tree/