sum of left leaves in a tree(leetcode).

 sum of left leaves in a tree(leetcode).

 class Solution {
public:
    
    
    int sumOfLeftLeaves(TreeNode* root)
    {
        queue<TreeNode *>q;
        int sum=0;
        if(root==NULL)
            return 0;
        else if(root->left==NULL && root->right==NULL)
            return 0;
        else
        {        
        q.push(root);
        while(!q.empty())
        {
            TreeNode * x;
            x=q.front();
            q.pop();
            if(x->left!=NULL)
            {
            if(x->left->left==NULL && x->left->right==NULL)
                sum=sum+x->left->val;
            }
            if(x->left!=NULL)
                q.push(x->left);
            if(x->right!=NULL)
                 q.push(x->right);  
            
            
        }
            return sum;
        }
            
        
        
    }
};