Formatted question description: https://leetcode.ca/all/404.html
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
// 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);
}
};
Java
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int sumOfLeftLeaves(TreeNode root) {
if (root == null || root.left == null && root.right == null)
return 0;
int sum = 0;
Queue<TreeNode> queue = new LinkedList<TreeNode>();
queue.offer(root);
while (!queue.isEmpty()) {
TreeNode node = queue.poll();
TreeNode left = node.left, right = node.right;
if (isLeaf(left))
sum += left.val;
if (left != null)
queue.offer(left);
if (right != null)
queue.offer(right);
}
return sum;
}
public boolean isLeaf(TreeNode node) {
if (node == null)
return false;
if (node.left == null && node.right == null)
return true;
return false;
}
}