左叶子之和

题目

题源

代码

深度优先：

class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        return root != null ? dfs(root) : 0;
    }
    private int dfs(TreeNode node) {
        int ans = 0;
        if (node.left != null) {
            ans +=  isLeafNode(node.left) ? node.left.val : dfs(node.left);
        }
        if (node.right != null && !isLeafNode(node.right)) {
            ans += dfs(node.right);
        }
        return ans;
    }
    private boolean isLeafNode(TreeNode node) {
        return node.left == null && node.right == null;
    }
}

广度优先：

class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        if (root == null) return 0;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        int ans = 0;
        while (!queue.isEmpty()) {
            TreeNode node = queue.poll();
            if (node.left != null) {
                if (isLeafNode(node.left)) {
                    ans += node.left.val;
                } else {
                    queue.offer(node.left);
                }
            }
            if (node.right != null && !isLeafNode(node.right)) {
                queue.offer(node.right);
            } 
        }
        return ans;
    }
   
    private boolean isLeafNode(TreeNode node) {
        return node.left == null && node.right == null;
    }
}