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by Sumit Chourasia | Oct 06, 2020 | Category :coding | Tags : algorithm binary-tree data-structure easy leetcode tree

Sum of Left Leaves - Tree - Easy - LeetCode

Sum of Left Leaves - Tree - Easy - 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.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
public class Solution {
    public int SumOfLeftLeaves(TreeNode root) {
        int res = Helper(root,false);
        return res;
    }
    
    private int Helper(TreeNode root, bool isLeft){
        int sum = 0;
        if(root == null){
            return sum;
        }
                
        if(root.left==null && root.right==null && isLeft){
            sum += root.val;
        }
        
        sum += Helper(root.left, true);
        sum += Helper(root.right, false);
        return sum;
    }
}

Time Complexity: O(n)

Space Complexity: O(1)