求树最后一层最左的结点，采用queue层遍历，但是是从右往左，保证最后一个即所求
/**
* 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 findBottomLeftValue(TreeNode* root) {
queue<TreeNode*> q;
TreeNode* now = root;
q.push(now);
while(!q.empty()) {
now = q.front();
q.pop();
if(now->right != NULL)
q.push(now->right);
if(now->left != NULL)
q.push(now->left);
}
return now->val;
}
};
