513. Find Bottom Left Tree Value

/**
 * 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) {
        int ans = 0;
        if(!root)
        {
            return 0;
        }
        queue<TreeNode*> q;
        q.push(root);

        while(!q.empty())
        {
            int size = q.size();

            for(int i=0; i<size; i++)
            {
                TreeNode* front = q.front();
                q.pop();

                //first value of a level
                if(i == 0)
                {
                    ans = front -> val;
                }

                if(front -> left) q.push(front -> left);
                if(front -> right) q.push(front -> right);
            }
        }

        return ans;
    }
};