求一棵树的最大深度

思路：广度优先搜索即可

class Solution {
public:
    int maxDepth(TreeNode *root) {
        int depth = 0;
        if (!root)
            return depth;
        queue<TreeNode*> nodeQue;
        nodeQue.push(root);
        while (!nodeQue.empty())
        {
            depth++;
            int qSize = nodeQue.size();
            for (size_t i = 0; i < qSize; i++)
            {
                if (nodeQue.front()->left)
                    nodeQue.push(nodeQue.front()->left);
                if (nodeQue.front()->right)
                    nodeQue.push(nodeQue.front()->right);
                nodeQue.pop();
            }
        }
        return depth;
    }
};

Maximum Depth of Binary Tree

原文：http://www.cnblogs.com/flyjameschen/p/f7d1f1fbb1edbecffb39ada376fa6f60.html