思路

一道巨简单的题目，单纯想练习一下递归。

复杂度

时间复杂度O(n)
空间复杂度最坏情况O(n)

代码

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */

public class Solution {
    /**
     * @param root: the root of the binary tree
     * @return: An integer
     */
    public int leafSum(TreeNode root) {
        // write your code here
        if(root == null)    return 0;
        if(root.left == null && root.right == null) {
            return root.val;
        }
        
        int sum = 0;
        sum += leafSum(root.left);
        sum += leafSum(root.right);
        return sum;
    }
}