513 - Find Bottom Left Tree Value

#medium

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

Example 1:

Input: root = [2,1,3]
Output: 1

Example 2:

Input: root = [1,2,3,4,null,5,6,null,null,7]
Output: 7

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int findBottomLeftValue(TreeNode* root) {
        queue<TreeNode*> que;
        que.push(root);
        int left_value;
        while ( !que.empty() ) {
            int que_size = que.size();
            for ( int i = 0; i < que_size; i++ ) {
                TreeNode * node = que.front();
                que.pop();
                if ( i == 0 ) left_value = node -> val;
                if ( node -> left != NULL ) que.push( node -> left );
                if ( node -> right != NULL ) que.push( node -> right );
            }

        }

        return left_value;

    }
};