404. Sum of Left Leaves

404. Sum of Left Leaves (Easy)

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.

Related Topics:
Tree

Solution 1. DFS

// OJ: https://leetcode.com/problems/sum-of-left-leaves
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(H)
class Solution {
private:
    int dfs(TreeNode *root, bool isLeftChild) {
        if (!root) return 0;
        if (!root->left && !root->right && isLeftChild) return root->val;
        return dfs(root->left, true) + dfs(root->right, false);
    }
public:
    int sumOfLeftLeaves(TreeNode* root) {
        return dfs(root, false);
    }
};