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LeetCode 404: Sum of Left Leaves Solution

Master LeetCode problem 404 (Sum of Left Leaves), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

Problem Explanation

Explanation:

To solve this problem, we can perform a depth-first traversal of the binary tree. While traversing, we keep track of whether a node is a left child and also whether it is a leaf node. If a node is a left child and a leaf node, we add its value to the sum.

Algorithm:

  1. Initialize a variable sum to store the sum of left leaves and start a depth-first traversal of the tree.
  2. At each node, check if it is a leaf node and a left child. If it is, add its value to the sum.
  3. Recursively traverse the left and right subtrees, passing the information about whether the current node is a left child or not.
  4. Return the sum calculated during the traversal.

Time Complexity: O(n) - where n is the number of nodes in the binary tree. Space Complexity: O(h) - where h is the height of the binary tree (recursion stack space).

:

Solution Code

class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        if (root == null) return 0;
        
        int sum = 0;
        if (root.left != null && root.left.left == null && root.left.right == null) {
            sum += root.left.val;
        }
        
        sum += sumOfLeftLeaves(root.left) + sumOfLeftLeaves(root.right);
        
        return sum;
    }
}

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