404. Sum of Left Leaves（LeetCode）

Find the sum of all left leaves in a given binary tree.

Example:

    3
   / \
  9  20
    /  \
   15   7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.
注：只求叶子的和！！

/**
 * 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 sumOfLeftLeaves(TreeNode* root) {
        if (root == NULL)
            return 0;
        else
        return sumleft(root);
    }
    int sumleft(TreeNode* root)
    {
        int sum=0;
        stack<TreeNode*> sta;
        sta.push(root);
        while (sta.size())
        {
            TreeNode* pNode = sta.top();
            sta.pop();
            if (pNode->right)
                sta.push(pNode->right);
            if (pNode->left)
            {
                sta.push(pNode->left);
                if (pNode->left->left == NULL&&pNode->left->right == NULL)
                sum += pNode->left->val;
            }
            
        }
        return sum;
    }
};