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)
