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.

分析：广搜，层序遍历，保存每层的第一个值，最后的即为所求值。

/**
 * 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) {
        int result = root->val;
        queue<TreeNode *> q;
        q.push(root);
        TreeNode* temp;
        while (!q.empty()) {
            int size = q.size();
            result = q.front()->val;
            while (size--) {
                temp = q.front();
                q.pop();
                if (temp->left != NULL) q.push(temp->left);
                if (temp->right != NULL) q.push(temp->right);
            }
        }
        return result;
    }
};