BFS + 队列
java
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public int sumOfLeftLeaves(TreeNode root) {
int sum = 0;
Deque<TreeNode> queue = new LinkedList<TreeNode>();
if(root == null){
return sum;
}
queue.offer(root);
while(!queue.isEmpty()){
int size = queue.size();
for(int i = 0; i < size; i++){
TreeNode node = queue.poll();
if(node.left != null){
queue.offer(node.left);
// 注意题目要求是求左叶子之和,所以需要判断一下左节点是否为叶子节点
if(node.left.left == null && node.left.right == null){
sum += node.left.val;
}
}
if(node.right != null){
queue.offer(node.right);
}
}
}
return sum;
}
}