404. Sum of Left Leaves

• Difficulty: Easy

• Topics: Tree

• Similar Questions:

Problem:

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. </pre> </p>

Solutions:

/**
 * 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)  return 0;
        int sum = 0;
        if (root->left)
            helper(root->left, sum, true);
        if (root->right) 
            helper(root->right, sum, false);
        return sum;
    }

private:
    void helper(TreeNode* root, int& sum, bool left) {
        if (!root->left && !root->right && left) {
            sum += root->val;
        }

        if (root->left) {
            helper(root->left, sum, true);
        }

        if (root->right) {
            helper(root->right, sum, false);
        }

    }

};