404. Sum of Left Leaves (Easy)
https://leetcode.com/problems/sum-of-left-leaves/
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.
Solutions
class Solution {
public int sumOfLeftLeaves(TreeNode root) {
if (root == null) {
return 0;
}
List<TreeNode> lleafs = new ArrayList<>();
dfs(root, lleafs);
int ans = 0;
for (TreeNode leaf : lleafs) {
ans += leaf.val;
}
return ans;
}
private void dfs(TreeNode root, List<TreeNode> lleafs) {
if (root == null) {
return;
}
if (root.left != null && root.left.left == null && root.left.right == null) {
lleafs.add(root.left);
} else {
dfs(root.left, lleafs);
}
dfs(root.right, lleafs);
}
}