LeetCode - 513 - Find Bottom Left Tree Value

Given a binary tree, find the leftmost value in the last row of the tree.

Example 1:

Input:

2
/ \
1   3

Output:
1

Example 2: 

Input:

1
/ \
2   3
/   / \
4   5   6
/
7

Output:
7

Note: You may assume the tree (i.e., the given root node) is not NULL.

找到最底层最左边的叶子节点。

利用队列，时间复杂度O(n)，空间复杂度O(n)

/**
* 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;
q.push(root);
int ans = 0;
while (!q.empty()) {
TreeNode* cur = q.front();
if (cur->right) q.push(cur->right);
if (cur->left) q.push(cur->left);
q.pop();
if (q.empty()) ans = cur->val;
}
return ans;
}
};